cmd/compile: remove walkinrange optimization

The walkinrange optimization has been superseded by CL 165998.

Has a small positive impact on binary sizes:

compilecmp master -> HEAD
master (e37cc298): cmd/compile: optimize integer-in-range checks
HEAD (1a70680a34): cmd/compile: remove walkinrange optimization
platform: linux/amd64

file      before    after     Δ       %
addr2line 4329144   4325048   -4096   -0.095%
api       6060970   6056874   -4096   -0.068%
asm       5196905   5192809   -4096   -0.079%
cgo       4898769   4890577   -8192   -0.167%
compile   20222193  20209713  -12480  -0.062%
cover     5331580   5323388   -8192   -0.154%
dist      3732778   3728682   -4096   -0.110%
doc       4748488   4740296   -8192   -0.173%
link      6707380   6695092   -12288  -0.183%
nm        4278685   4274589   -4096   -0.096%
pack      2305038   2300942   -4096   -0.178%
pprof     14874834  14870738  -4096   -0.028%
test2json 2849221   2845125   -4096   -0.144%
vet       8393173   8384981   -8192   -0.098%
go        15205572  15193284  -12288  -0.081%
total     131812292 131709700 -102592 -0.078%

Updates #30645.

Change-Id: I42d74481652c90fef1a9bc58c70836e42c9b1c4b
Reviewed-on: https://go-review.googlesource.com/c/go/+/221802


Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>