memory: plug a leak, by freeing the cutbuffer after a bracketed paste

Also, remove an unneeded assignment -- the 'cutbottom' variable is
needed only when consecutives cuts (^K) or copies (M-6) are made.

src/nano.c

@@ -1483,10 +1483,9 @@ void suck_up_input_and_paste_it(void)
 			beep();
 	}
 
-	cutbottom = line;
-
 	paste_text();
 
+	free_lines(cutbuffer);
 	cutbuffer = was_cutbuffer;
 }
 #endif