Since ce03a862372a6f36d2fcf80dc80052aa155fcae8 and 427bb1cc1b09ea68b8a13a667810681ba4074f6b, mips64 support for POSIX is orphaned. Remove any POSIX_mips64 code and other code we missed in those commits. --------- Signed-off-by: Minsoo Choo <minsoochoo0122@proton.me>