c_execution: remove unused source_suffix argument to GCCToolchain #3066

Job	Run time
Tests for downstream project Firedrake	15m 32s
Documentation	2m 6s
Tests for downstream project arraycontext	4m 30s
Tests for downstream project meshmode	11m 3s
Conda Examples	2m 27s
Flake8	27s
Tests for downstream project grudge	7m 41s
Tests for downstream project pytential	34m 47s
Mypy	4m 24s
Tests for downstream project pytato	5m 21s
Pylint	2m 25s
Conda Pytest (ubuntu-latest)	4m 14s
Conda Pytest with Intel CL	4m 16s
Conda Pytest (macos-latest)	6m 59s
Conda Pytest without arg check	4m 15s
Conda Pytest Twice (for cache behavior)	5m 22s
Validate CITATION.cff	6s
	1h 55m 55s

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