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Allow machine dce to remove uses in the same instruction

Description

Allow machine dce to remove uses in the same instruction

Machine DCE cannot remove a dead definition if there are non-dbg uses.
A use however can be in the same instruction:

dead %0 = INST %0

Such instructions sometimes created by Detect dead lanes pass.

Allow this instruction to be deleted despite the use if the only use
belongs to the same instruction.

Differential Revision: https://reviews.llvm.org/D59565