Remove unused FindCTK.cmake module

Since CTK targets are exported into a CTKConfig.cmake file, there is
no need for such module. It would simply add extra maintenance work
without real advantage.

See #397
Merge remote-tracking branch 'jcfr/397-remove-unused-find-ctk-module'

* jcfr/397-remove-unused-find-ctk-module:
  Remove unused FindCTK.cmake module