[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
(cherry picked from commit 960cbc53ca170c8c605bf83fa63b49ab27a56f65)