git-gui: Remove spurious newline in untracked file display.

This newline is stupid; it doesn't get put here unless the file
is very large, and then its just sort of out of place.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -657,7 +657,6 @@ proc show_diff {path w {lno {}}} {
 				$ui_diff insert end \
 "* Untracked file is $sz bytes.
 * Showing only first $max_sz bytes.
-
 " d_@
 			}
 			$ui_diff insert end $content