Revert "[clangd] Add tweak to override pure virtuals (#139348)" (#150404)
This reverts commit 7355ea3f6b214d1569da43d02f9a166ff15012e6.
Buildbot failures:
UBsan
https://lab.llvm.org/buildbot/#/builders/25/builds/10010
Fast
https://lab.llvm.org/buildbot/#/builders/169/builds/13150