All but 3 callsites of this function in the standard library and
compiler were unnecessary and were removed in faf2fd18.

In this commit, the remaining 3 callsites are removed. One of them
turned out to also be unnecessary and has been replaced by slicing
directly with the length..

The 2 remaining callsites were in the very pointer-math heavy
std/os/linux/vdso.zig code which should perhaps be refactored to better
utilize slices. These 2 callsites are replaced with a plain
@ptrCast([*:0]u8, ptr) though could likely use std.mem.sliceTo() if the
surrounding code was refactored.