Revert of Speedup stringsearch for two byte strings (patchset #3 id:40001 of https://codereview.chromium.org/1303033012/ )

Reason for revert:
[Sheriff] Breaks fuzzer and msan:
http://build.chromium.org/p/client.v8/builders/V8%20Fuzzer/builds/4773

Repro with:
tools/fuzz-harness.sh out/Debug/d8
(in a ninja Debug build)

Msan:
http://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20arm64%20-%20sim%20-%20MSAN/builds/4097

Original issue's description:
> Speedup stringsearch for two byte strings
>
> Uses the lower byte with memchr which is
> significantly faster than a naive compare
>
> Performance difference with bench (http://hastebin.com/xuxexataso.js):
>
> old                             new
>
> single character                single character
> Κ found at 922                  Κ found at 922
> 3324                            616
> ㎡ found at 13217               ㎡ found at 13217
> 42366                           4931
> က found at 4096                 က found at 4096
> 13369                           9836
> ＀ found at 65280                ＀ found at 65280
> 207472                          36149
> ﾥ found at 65445                ﾥ found at 65445
> 209344                          36666
>   found at 8197                   found at 8197
> 26731                           11757
> 倂 found at 20482               倂 found at 20482
> 66071                           17193
>
> linear search                   linear search
> ΚΛ found at 922                 ΚΛ found at 922
> 4112                            504
> ㎡㎢ found at 13217             ㎡㎢ found at 13217
> 55105                           5119
> ﾥﾦ found at 65445               ﾥﾦ found at 65445
> 268016                          35496
>
> linear + bmh search             linear + bmh search
> ΚΛΜΝΞΟΠΡ found at 922           ΚΛΜΝΞΟΠΡ found at 922
> 2897                            522
> ﾥﾦﾧﾨﾩﾪﾫﾬ found at 65445         ﾥﾦﾧﾨﾩﾪﾫﾬ found at 65445
> 167687                          158465
>
> Committed: https://crrev.com/fced280f37588f8a232a414201276e053117e9ea
> Cr-Commit-Position: refs/heads/master@{#30587}

TBR=danno@chromium.org,mstarzinger@chromium.org,jkummerow@chromium.org,karl@skomski.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/1331433002

Cr-Commit-Position: refs/heads/master@{#30588}