[llvm-profgen] Remove target triple check to allow for more targets

Llvm-profgen internally uses the llvm libraries and the MCDesc interface to do disassembling and symblization and it never checks against target-specific instruction operators. This makes it quite transparent to targets and a first attempt for an aarch64 binary just works. Therefore I'm removing the unnecessary triple check to unblock for new targets.

Reviewed By: wenlei

Differential Revision: https://reviews.llvm.org/D153449