added a function to remove flags #850

Job	Run time
Test CUDA support	30s
Test (stable)	41s
Rustfmt	20s
Test (beta)	46s
Test (nightly)	44s
Test (linux32)	1m 1s
MSRV (ubuntu-latest)	3m 36s
Test (macos)	1m 38s
MSRV (windows-latest)	4m 27s
Test (aarch64-ios)	1m 10s
Test (win32)	1m 53s
Test (win64)	2m 1s
Test (mingw32)	1m 36s
Test (mingw64)	2m 2s
Test (windows-2019)	1m 44s
Test (windows-aarch64, windows-latest, stable, aarch64-pc-windows-msvc, --no-run)	1m 38s
	25m 47s

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