[HWASAN] Remove UAR tag branch !ClUARRetagToZero

This is leftover from older version of HWASAN.
The current HWASAN assumes that the new stack
frames are tagged with zeroes, which make getNextTagWithCall
or StackTag ^ TagMaskByte unusable.

Reviewed By: kstoimenov, eugenis

Differential Revision: https://reviews.llvm.org/D149220