patch 8.1.2406: leaking memory in test_paste and test_registers

Problem:    Leaking memory in test_paste and test_registers.
Solution:   Free the old title.  Don't copy expr_line.
diff --git a/src/term.c b/src/term.c
index 57384f4..b0ab7c6 100644
--- a/src/term.c
+++ b/src/term.c
@@ -2106,6 +2106,8 @@
 {
     int	    i;
 
+    // Note: Valgrind may report a leak here, because the library keeps one
+    // buffer around that we can't ever free.
     i = TGETENT(tbuf, term);
     if (i < 0		    // -1 is always an error
 # ifdef TGETENT_ZERO_ERR