Don't call SourceFormatterSelectionEdit::resetUi() redundantly

When Configure KDevelop dialog is shown, this function is called once
for each source formatter plugin, plus one more time, which amounts to 3
times with the 2 enabled by default plugins. loadSettings() is always
called after the constructor, so let it make the one resetUi() call.
Note that resetUi() should not be called before loadSettings(), because
user-selected formatters and styles cannot be displayed before
loadSettings() reads them from configuration.