Don't use informative text for message box

The informative text is meant to be additional information, not the main
information.  If you use informative text without using regular text, it
causes the message box to get all squishy.

obs/window-basic-main.cpp

@@ -843,8 +843,9 @@ bool OBSBasic::QueryRemoveSource(obs_source_t source)
 	text.replace("$1", QT_UTF8(name));
 
 	QMessageBox remove_source;
-	remove_source.setInformativeText(text);
-	QAbstractButton *Yes = remove_source.addButton(QTStr("Yes"), QMessageBox::YesRole);
+	remove_source.setText(text);
+	QAbstractButton *Yes = remove_source.addButton(QTStr("Yes"),
+			QMessageBox::YesRole);
 	remove_source.addButton(QTStr("No"), QMessageBox::NoRole);
 	remove_source.setIcon(QMessageBox::Question);
 	remove_source.setWindowTitle(QTStr("ConfirmRemove.Title"));