Remove MSVC 2015 workaround #7678

Job	Run time
mingw (mingw64)	4m 34s
mingw (ucrt64)	4m 5s
build (windows-2019, Win32, v142, 17, Debug)	1m 16s
build (windows-2019, Win32, v142, 17, Release)	3m 44s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	4m 0s
build (windows-2019, Win32, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	3m 4s
build (windows-2019, x64, v141, 14, Debug)	2m 1s
build (windows-2019, x64, v141, 14, Release)	3m 41s
build (windows-2019, x64, v141, 17, Debug)	2m 14s
build (windows-2019, x64, v141, 17, Release)	2m 17s
build (windows-2019, x64, v142, 17, Debug)	2m 13s
build (windows-2019, x64, v142, 17, Release)	2m 15s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Debug)	1m 59s
build (windows-2019, x64, v142, 17, -DBUILD_SHARED_LIBS=ON, Release)	3m 35s
build (windows-2019, x64, v142, 20, Debug)	1m 31s
build (windows-2019, x64, v142, 20, Release)	6m 24s
build (windows-2022, x64, v143, Debug, 20)	1m 38s
	50m 31s

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