fs: remove duplicate fd validation in sync functions #2314

Job	Run time
Build slim tarball	1m 43s
aarch64-linux: with shared libraries	1h 0m 44s
x86_64-linux: with shared libraries	1h 17m 25s
x86_64-darwin: with shared libraries	1h 33m 30s
aarch64-darwin: with shared libraries	1h 17m 7s
	5h 10m 29s

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