[mlir] Remove 'valuesToRemoveIfDead' from PatternRewriter API

Summary:
Remove 'valuesToRemoveIfDead' from PatternRewriter API. The removal
functionality wasn't implemented and we decided [1] not to implement it in
favor of having more powerful DCE approaches.

[1] https://github.com/tensorflow/mlir/pull/212

Reviewers: rriddle, bondhugula

Reviewed By: rriddle

Subscribers: liufengdb, mehdi_amini, rriddle, jpienaar, burmako, shauheen, antiagainst, nicolasvasilache, arpith-jacob, mgester, lucyrfox, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D72545