[DAGCombine] Remove dead node when it is created by getNegatedExpression

We hit the compiling time reported by https://bugs.llvm.org/show_bug.cgi?id=46877
and the reason is the same as D77319. So we need to remove the dead node we created
to avoid increase the problem size of DAGCombiner.

Reviewed By: Spatel

Differential Revision: https://reviews.llvm.org/D86183