[clangd] Drop template argument lists from completions followed by <

Now, given `template <typename T> foo() {}` when user types `fo^<int>()` the
completion snippet will not contain `<int>()`.

Also, when the next token is opening parenthesis (`(`) and completion snippet
contains template argument list, it is still emitted.

This patch complements D81380.

Related issue: https://github.com/clangd/clangd/issues/387

Reviewed By: kadircet

Differential Revision: https://reviews.llvm.org/D89870