Remove ErrFsExistsDiffSize error on incompatible parameter

[jacobwolfaws]

Is this a bug fix or adding new feature?
bug fix
What is this PR about? / Why do we need it?
This PR is meant to address this issue: #288
Right now an incompatible parameter error (like specifying throughput for SCRATCH_2), returns a ErrFsExistsDiffSize error. This error is both 1) wrong and 2) not descriptive for users to mitigate this issue. This PR just removes the if statement completely & associated function completely, so users get a descriptive error output. ex:

"GRPC error" err=<
	rpc error: code = Internal desc = Could not create volume "pvc-example_pvc": CreateFileSystem failed: IncompatibleParameterError: The storage throughput can not be specified for a lustre file system with DeploymentType=SCRATCH_2
	{
	  RespMetadata: {
	    StatusCode: 400,
	    RequestID: "example_request"
	  },
	  Message_: "The storage throughput can not be specified for a lustre file system with DeploymentType=SCRATCH_2"
	}
 >

What testing is done?

• tested with storageclass that tries to specify throughput for scratch
• sanity testing

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jacobwolfaws

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[jacobwolfaws]

/retest

stuck in pending, trying this to mitigate

[jacobwolfaws]

/test all

[jacobwolfaws]

kubernetes/test-infra#29622 Appears to be related to the stuck tests

[jacobwolfaws]

/retest

[khoang98]

/lgtm