don't crash when an unused operator import ends in `.` (#2123)

* replace head with safer uncons

* if empty, stay empty

* add test for removal of operators ending with '.'

* make remove-import-actions tests pass

* add more tests and debug output for modifyBinding

* implement reviewers suggestions

* restore ghcide/bench/example/HLS

Co-authored-by: Pepe Iborra <pepeiborra@gmail.com>