richcombo plugin: Removes extra quote from template string.

This was resulting in invalid markup. (Found with help from [HTMLHint](/yaniswang/HTMLHint). :candy:)
Apparently the bug has been around in some form [since early 2010](/ckeditor/ckeditor-dev/commit/e2070a8220c13de7e7b38e35368e98a452ff958d#diff-72cbfcc1b6324132f021fda69da2b56dL116)..!

This commit also removes a duplicate `hidefocus` attribute.