remove files from /usr/local

Rename `search` and `highlight` to `mint-search` and `mint-highlight` to avoid package conflicts with  [highlight](http://packages.ubuntu.com/trusty/highlight) and [sphinxsearch](http://packages.ubuntu.com/trusty/sphinxsearch).
Mint's `apt` will be installed into `/usr/local/bin` via postinst maintainer script.
I've also renamed prerm to postrm (update-rc.d must be called in postrm).