SCRIPTS: git-show-backports: make -m most only show the left branch

We've never used the output of the rightmost branch with this tool,
and it systematically causes two identical outputs making the job
harder during backport sessions. Let's simply remove the right part
when it's identical to the left one. This also adds a few line feeds
to make the output more readable.
diff --git a/scripts/git-show-backports b/scripts/git-show-backports
index 4c6ccee..d01f92c 100755
--- a/scripts/git-show-backports
+++ b/scripts/git-show-backports
@@ -249,12 +249,18 @@
 		echo "No missing commit to apply."
 	elif [ -n "$MISSING" ]; then
 		echo
+		echo
 		echo "In order to show and/or apply all leftmost commits to current branch :"
 		echo "   git show ${left_commits[@]}"
+		echo
 		echo "   git cherry-pick -sx ${left_commits[@]}"
 		echo
-		echo "In order to show and/or apply all rightmost commits to current branch :"
-		echo "   git show ${right_commits[@]}"
-		echo "   git cherry-pick -sx ${right_commits[@]}"
+		if [ "${left_commits[*]}" != "${right_commits[*]}" ]; then
+			echo "In order to show and/or apply all rightmost commits to current branch :"
+			echo "   git show ${right_commits[@]}"
+			echo
+			echo "   git cherry-pick -sx ${right_commits[@]}"
+			echo
+		fi
 	fi
 )