[clangd] DefineOutline: removes static token from static CXXMethodDecl

Summary: Removes the `static` token when defining a function out of line if the function is a `CXXMethodDecl`

Reviewers: sammccall, kadircet, hokein

Reviewed By: kadircet

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, usaxena95, cfe-commits

Tags: #clang, #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D77534