Remove "instrumentLong" from extracted part

1. Open bach-bc2 demo score
2. File > Parts...
3. Create part for trumpet

Expected behavior: The instrumentLong should be removed from the beginning of the staff since the "Part Title" is already displayed in large text on the top left corner. The instrumentLong should be replaced with about 10 spaces to give the first line of the part an indentation.

Actual behavior: instrumentLong is displayed.

Discussion: The instrumentLong should be removed (and replaced with spaces) if the following two conditions are met: a "Part Title" is specified in the part dialog and the resulting part contains only one instrument. In all other cases the instrumentLong should not be removed.