git-gui: Correct line wrapping for too many branch message

Since Tk automatically wraps lines for us in tk_messageBox
widgets we don't need to try to wrap them ourselves.  Its
actually worse that we linewrapped this here in the script,
as not all fonts will render this dialog nicely.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -2907,12 +2907,9 @@ You are merging $revcnt branches at once.  This requires using the octopus merge
 			-parent $w \
 			-message "Too many branches selected.
 
-You have requested to merge $revcnt branches
-in an octopus merge.  This exceeds Git's
-internal limit of 15 branches per merge.
+You have requested to merge $revcnt branches in an octopus merge.  This exceeds Git's internal limit of 15 branches per merge.
 
-Please select fewer branches.  To merge more
-than 15 branches, merge the branches in batches.
+Please select fewer branches.  To merge more than 15 branches, merge the branches in batches.
 "
 		return
 	}