git: removal of `bower.json`

* Removes auto-generated `bower.json` that is already present in
  `.gitignore` anyway.

* NOTE when upgrading, keep your own local copy of the file, or
  regenerate it anew via usual procedures.
  (`inveniomanage bower -i bower-base.json > bower.json`)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>