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/os_unix.c b/src/os_unix.c
index 90c5aed..7e78209 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -1963,6 +1963,10 @@
 	    retval = TRUE;
 	    if (!test_only)
 	    {
+		if (get_title)
+		    vim_free(oldtitle);
+		else
+		    vim_free(oldicon);
 		if (text_prop.encoding == XA_STRING && !has_mbyte)
 		{
 		    if (get_title)