iox-#2011 Remove gcc 5.4 and std_header_check.sh from CI #7606

Job	Run time
pre-flight-check	36s
build-test-windows	5m 5s
build-test-ubuntu-with-address-sanitizer-gcc-latest	5m 22s
build-test-unix-with-freebsd	5m 6s
run-integration-test	5m 22s
build-test-ubuntu	5m 22s
build-test-macos-with-address-sanitizer	5m 20s
build-test-ubuntu-bazel	5m 19s
build-test-ubuntu-with-address-sanitizer-clang-latest	5m 22s
build-test-ubuntu-with-thread-sanitizer-clang-latest	5m 21s
coverage-and-docs	5m 21s
	53m 36s

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