[lldb/Utils] Remove vim-lldb

The vim-lldb plugin is unmaintained and doesn't work with a recent vim
installation that uses Python 3. This removes it from the LLDB
repository. The code is still available under lldb-tools on GitHub like
we did with for lldb-mi. (https://github.com/lldb-tools/vim-lldb)

Differential revision: https://reviews.llvm.org/D72541