patch 8.1.2107: various memory leaks reported by asan

Problem:    Various memory leaks reported by asan.
Solution:   Free the memory. (Ozaki Kiichi, closes #5003)
diff --git a/src/terminal.c b/src/terminal.c
index 4f2b8bb..52487a3 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -4602,6 +4602,7 @@
     }
 
     ga_clear(&ga_text);
+    ga_clear(&ga_cell);
     vim_free(prev_char);
 
     return max_cells;
@@ -4733,7 +4734,7 @@
 	    buf = curbuf;
 	    while (!(curbuf->b_ml.ml_flags & ML_EMPTY))
 		ml_delete((linenr_T)1, FALSE);
-	    ga_clear(&curbuf->b_term->tl_scrollback);
+	    free_scrollback(curbuf->b_term);
 	    redraw_later(NOT_VALID);
 	}
     }