Remove sending_queue from AWS Prometheus Remote Write Exporter

[rakyll]

This is a follow up of open-telemetry/opentelemetry-collector#2951.

Fixes #3163.

[rakyll]

cc @anuraaga

[bogdandrutu]

Tests failed:

running go unit test ./... + coverage in /home/circleci/project/exporter/awsprometheusremotewriteexporter
--- FAIL: TestLoadConfig (0.01s)
    config_test.go:104: 
        	Error Trace:	config_test.go:104
        	Error:      	Not equal: 
        	            	expected: &awsprometheusremotewriteexporter.Config{Config:prometheusremotewriteexporter.Config{ExporterSettings:(*config.ExporterSettings)(0xc00066e260), TimeoutSettings:exporterhelper.TimeoutSettings{Timeout:5000000000}, QueueSettings:exporterhelper.QueueSettings{Enabled:false, NumConsumers:0, QueueSize:0}, RetrySettings:exporterhelper.RetrySettings{Enabled:true, InitialInterval:10000000000, MaxInterval:60000000000, MaxElapsedTime:600000000000}, Namespace:"test-space", ExternalLabels:map[string]string{"key1":"value1", "key2":"value2"}, HTTPClientSettings:confighttp.HTTPClientSettings{Endpoint:"http://localhost:9009", TLSSetting:configtls.TLSClientSetting{TLSSetting:configtls.TLSSetting{CAFile:"/var/lib/mycert.pem", CertFile:"", KeyFile:""}, Insecure:false, InsecureSkipVerify:false, ServerName:""}, ReadBufferSize:0, WriteBufferSize:524288, Timeout:5000000000, Headers:map[string]string{"prometheus-remote-write-version":"0.1.0", "x-scope-orgid":"234"}, CustomRoundTripper:(func(http.RoundTripper) (http.RoundTripper, error))(nil)}}, AuthConfig:awsprometheusremotewriteexporter.AuthConfig{Region:"us-west-2", Service:"service-name", RoleArn:"arn:aws:iam::123456789012:role/IAMRole"}}
        	            	actual  : &awsprometheusremotewriteexporter.Config{Config:prometheusremotewriteexporter.Config{ExporterSettings:(*config.ExporterSettings)(0xc00066ec80), TimeoutSettings:exporterhelper.TimeoutSettings{Timeout:5000000000}, QueueSettings:exporterhelper.QueueSettings{Enabled:true, NumConsumers:2, QueueSize:10}, RetrySettings:exporterhelper.RetrySettings{Enabled:true, InitialInterval:10000000000, MaxInterval:60000000000, MaxElapsedTime:600000000000}, Namespace:"test-space", ExternalLabels:map[string]string{"key1":"value1", "key2":"value2"}, HTTPClientSettings:confighttp.HTTPClientSettings{Endpoint:"http://localhost:9009", TLSSetting:configtls.TLSClientSetting{TLSSetting:configtls.TLSSetting{CAFile:"/var/lib/mycert.pem", CertFile:"", KeyFile:""}, Insecure:false, InsecureSkipVerify:false, ServerName:""}, ReadBufferSize:0, WriteBufferSize:524288, Timeout:5000000000, Headers:map[string]string{"prometheus-remote-write-version":"0.1.0", "x-scope-orgid":"234"}, CustomRoundTripper:(func(http.RoundTripper) (http.RoundTripper, error))(nil)}}, AuthConfig:awsprometheusremotewriteexporter.AuthConfig{Region:"us-west-2", Service:"service-name", RoleArn:"arn:aws:iam::123456789012:role/IAMRole"}}
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -10,5 +10,5 @@
        	            	   QueueSettings: (exporterhelper.QueueSettings) {
        	            	-   Enabled: (bool) false,
        	            	-   NumConsumers: (int) 0,
        	            	-   QueueSize: (int) 0
        	            	+   Enabled: (bool) true,
        	            	+   NumConsumers: (int) 2,
        	            	+   QueueSize: (int) 10
        	            	   },
        	Test:       	TestLoadConfig
FAIL

[codecov]

Codecov Report

Merging #3186 (73de434) into main (e663b59) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3186      +/-   ##
==========================================
- Coverage   91.93%   91.91%   -0.02%     
==========================================
  Files         493      493              
  Lines       23946    23946              
==========================================
- Hits        22014    22010       -4     
- Misses       1427     1429       +2     
- Partials      505      507       +2     

Flag	Coverage Δ
integration	63.35% <ø> (-0.06%)	⬇️
unit	90.93% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
exporter/signalfxexporter/dimensions/requests.go	82.35% <0.00%> (-3.93%)	⬇️
receiver/k8sclusterreceiver/watcher.go	95.29% <0.00%> (-2.36%)	⬇️

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[rakyll]

The test is passing now. PTAL.