Delete empty searcher.py file

The file `searcher.py` was added, as an empty file, four years ago in
[#2312](https://github.com/dbt-labs/dbt-core/pull/2312/files#diff-c8e9e62cf63356f44fe1a2b0272b239d7a650c57911477ed4549b15ee3de16fa).
Since then it has never been touched or added to. I'm not sure of the
initial purpose of the file as it never contained anything and I have not
found any documentation in reference to it. It's safe to say, it can go
away.