chore: Remove `fs` feature enabling `mod mount` (#1194) #4383

Job	Run time
Check (stable)	6m 5s
Check --no-default-features (nightly)	54s
Check nightly-only targets (nightly)	24s
Check selected Tier 3 platforms (nightly)	4m 56s
Rustfmt	13s
Check (nightly)	6m 16s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 10s
Check (1.63)	9m 59s
Test rustix_use_experimental_asm (s390x-linux)	1m 4s
Test (ubuntu)	42s
Test (ubuntu-20.04)	43s
Test use-libc (ubuntu)	47s
Test (i686-linux)	58s
Test use-libc (i686-linux)	57s
Test use-libc (aarch64-linux)	1m 23s
Test (aarch64-linux)	1m 11s
Test use-libc (powerpc64le-linux)	1m 12s
Test (powerpc64le-linux)	1m 4s
Test use-libc (riscv64-linux)	57s
Test (riscv64-linux)	1m 13s
Test (s390x-linux)	1m 4s
Test use-libc (s390x-linux)	59s
Test (arm-linux)	1m 7s
Test use-libc (arm-linux)	1m 3s
Test (ubuntu-stable)	46s
Test (i686-linux-stable)	1m 19s
Test (aarch64-linux-stable)	1m 15s
Test (riscv64-linux-stable)	1m 5s
Test (s390x-linux-stable)	1m 0s
Test (powerpc64le-linux-stable)	1m 12s
Test (arm-linux-stable)	1m 16s
Test (ubuntu-1.63)	1m 57s
Test (i686-linux-1.63)	2m 10s
Test (aarch64-linux-1.63)	2m 32s
Test (riscv64-linux-1.63)	2m 19s
Test (s390x-linux-1.63)	2m 24s
Test (powerpc64le-linux-1.63)	2m 25s
Test (arm-linux-1.63)	2m 19s
Test (macos-latest)	36s
Test (macos-12)	54s
Test (windows)	44s
Test (windows-2019)	58s
Test (musl)	45s
	1h 14m 17s

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