[ARM] Remove redundant BTI instructions for table jumps

A BTI instruction was previously inserted at the beginning of each block
that has its address stored in a jump table. Jump tables only emit
indirect jumps in ARM or Thumb1 modes. However, PACBTI is not supported
in these modes. As a result, BTI instructions emitted by jump tables are
redundant. Removing redundant BTI instructions improves the code size
and prevents potential gadgets.

Differential Revision: https://reviews.llvm.org/D144470