Do not ignore safeToRemove instructions with no users #351

Job	Run time
cache-kernels	20s
code-style	11s
result-viewer (14.x)	1m 17s
result-viewer (16.x)	1m 27s
result-viewer (18.x)	1m 32s
result-viewer (20.x)	56s
build-and-test (9, gcc-9, g++-9, OFF, true)	20m 34s
build-and-test (10, gcc-9, g++-9, OFF, true)	20m 36s
build-and-test (11, gcc-9, g++-9, OFF, true)	21m 30s
build-and-test (12, gcc-9, g++-9, OFF, true)	21m 23s
build-and-test (13, gcc-9, g++-9, OFF, true)	21m 40s
build-and-test (14, gcc-9, g++-9, OFF, true)	20m 35s
build-and-test (15, gcc-9, g++-9, OFF, true)	23m 13s
build-and-test (16, gcc-9, g++-9, OFF, true)	22m 28s
build-and-test (16, clang, clang++, OFF, true)	22m 27s
build-and-test (14, gcc-9, g++-9, ON, false)	2m 49s
	3h 22m 58s

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