Remove an unused import from imeinsetssourceconsumer.proto

This is a follow up CL to our previous CL [1], which deprecated

  ImeInsetsSourceConsumerProto.focused_editor.

With that change, editorinfo.proto no longer needs to be imported.

This CL is to remove a compile time warning.  There should be no
observable behavior change.

 [1]: I32fe3759b9aeb56c868f9abf42bab124b9b83374
      72de8ead

Bug: 118599175
Bug: 159201509
Bug: 167948123
Bug: 192412909
Test: presubmit
Change-Id: Id6c7b85270b25058b7c8411b6cb87da3dabe4926