[turbofan] remove redundant '& 0x1F' for shifts.

JavaScript shifts perform an implicit '& 0x1F' on their right operand, this
patch removes it when the underlying architecture already does it.

BUG=
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/732103002

Cr-Commit-Position: refs/heads/master@{#25438}