Add strength reduction rules to optimize

 CheckTaggedSigned(CheckTaggedSigned(x)) -> CheckTaggedSigned(x)

and

 CheckTaggedPointer(CheckTaggedPointer(x)) -> CheckTaggedPointer(x)

where we do some cleanup optimizations after loop peeling and redundancy
elimination, which can generate these constructs.

BUG=v8:5267

Review-Url: https://codereview.chromium.org/2336093002
Cr-Commit-Position: refs/heads/master@{#39366}