Revert "This should finally fix the problem, that the first time the...

Revert "This should finally fix the problem, that the first time the completion popup is shown, the first group is empty."

This reverts commit 51fb673e.

This completely breaks code completion with the simple word-based
code completion builtin to Katepart. Probably the issue would arise
for any code completion models which are not grouped at all.

Conflicts:
	part/completion/katecompletionmodel.cpp

CCBUG: 315189