[clangd] Strip the ' [some-check-name]' suffix from clang-tidy diagnostics....

[clangd] Strip the ' [some-check-name]' suffix from clang-tidy diagnostics. The check name is reported in Diagnostic.code.

Reviewers: kadircet

Subscribers: ilya-biryukov, ioeric, MaskRay, jkorous, arphaman, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D60819

llvm-svn: 358612