[NFC] Remove no-op code from x86AssemblyInspectionEngine::jmp_to_reg_p

Slava Gurevich noticed this dead code I wrote in jmp_to_reg_p
is never executed, is duplicated, and has comments that seem to
describe the opposite behavior.  Remove the dead code that cannot
be executed.

Differential Revision: https://reviews.llvm.org/D131029