regalloc: removes unnecessary Instruction.Uses

[mathetake]

This also early stops resetting IDedPool.

Zig stdlib

goos: darwin
goarch: arm64
pkg: github.com/tetratelabs/wazero
               │ old_zig.txt │           new_zig.txt            │
               │   sec/op    │   sec/op    vs base              │
Compilation-10    4.540 ± 0%   4.380 ± 1%  -3.51% (p=0.001 n=7)

               │ old_zig.txt  │          new_zig.txt          │
               │     B/op     │     B/op      vs base         │
Compilation-10   599.3Mi ± 0%   599.3Mi ± 0%  ~ (p=0.383 n=7)

               │ old_zig.txt │         new_zig.txt          │
               │  allocs/op  │  allocs/op   vs base         │
Compilation-10   288.0k ± 0%   288.0k ± 0%  ~ (p=0.805 n=7)

wazero compiled as a wasip1 binary

goos: darwin
goarch: arm64
pkg: github.com/tetratelabs/wazero
               │  old.txt   │             new.txt              │
               │   sec/op   │   sec/op    vs base              │
Compilation-10   2.264 ± 1%   2.224 ± 0%  -1.80% (p=0.001 n=7)

               │   old.txt    │            new.txt            │
               │     B/op     │     B/op      vs base         │
Compilation-10   337.3Mi ± 0%   337.3Mi ± 0%  ~ (p=0.318 n=7)

               │   old.txt   │           new.txt            │
               │  allocs/op  │  allocs/op   vs base         │
Compilation-10   593.7k ± 0%   593.6k ± 0%  ~ (p=0.456 n=7)

#2182