remove tools/update_glibc.zig

It has been replaced by https://github.com/ziglang/glibc-abi-tool/ and
should have been removed in 1442aa7dc039fd77c483862e37b099fe6d43f369.
5da013e39cAndrew Kelley committed on 12/15/2021, 4:44:44 AMparent20328e9
1 file changedLine totals unavailable