Clean up the physfs_rwops re-write #47

Job	Run time
build (ubuntu-latest, Release, gcc)	2m 38s
build (ubuntu-latest, Release, clang)	3m 5s
build (ubuntu-latest, Release, mingw-w64-gcc)	3m 25s
build (ubuntu-latest, Debug, gcc)	3m 11s
build (ubuntu-latest, Debug, clang)	2m 36s
build (ubuntu-latest, Debug, mingw-w64-gcc)	2m 32s
build (windows-latest, Release, cl)	5m 27s
build (windows-latest, Debug, cl)	4m 59s
build (macos-latest, Release, gcc)	4m 25s
build (macos-latest, Release, clang)	3m 46s
build (macos-latest, Debug, gcc)	3m 29s
build (macos-latest, Debug, clang)	3m 25s
	42m 58s

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