Remove lit feature object-emission

Summary: The lit feature object-emission was added because Hexagon did not support the integrated assembler, so some tests needed to be turned off with a Hexagon target. Hexagon now supports the integrated assembler, so this feature can be removed.

Reviewers: bcain, kparzysz, jverma, whitequark, JDevlieghere

Reviewed By: JDevlieghere

Subscribers: mehdi_amini, hiraditya, steven_wu, dexonsmith, arphaman, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73568