[pushed] Fix two out-of-date comments

[Tom Tromey]

While looking at psymtabs again, I noticed a couple of outdated
comments.  These days, psymtabs can be destroyed, as they are no
longer obstack-allocated.

gdb/ChangeLog
2020-08-28  Tom Tromey  <tom@tromey.com>

	* xcoffread.c (xcoff_end_psymtab): Update comment.
	* dbxread.c (dbx_end_psymtab): Update comment.
---
 gdb/ChangeLog   | 5 +++++
 gdb/dbxread.c   | 3 +--
 gdb/xcoffread.c | 3 +--
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/gdb/dbxread.c b/gdb/dbxread.c
index 2df9f5c4d04..e76bf702b38 100644
--- a/gdb/dbxread.c
+++ b/gdb/dbxread.c
@@ -2047,8 +2047,7 @@ dbx_end_psymtab (struct objfile *objfile, legacy_psymtab *pst,
       && pst->n_static_syms == 0
       && has_line_numbers == 0)
     {
-      /* Throw away this psymtab, it's empty.  We can't deallocate it, since
-         it is on the obstack, but we can forget to chain it on the list.  */
+      /* Throw away this psymtab, it's empty.  */
       /* Empty psymtabs happen as a result of header files which don't have
          any symbols in them.  There can be a lot of them.  But this check
          is wrong, in that a psymtab with N_SLINE entries but nothing else
diff --git a/gdb/xcoffread.c b/gdb/xcoffread.c
index a792c0fea2e..389678aa5b7 100644
--- a/gdb/xcoffread.c
+++ b/gdb/xcoffread.c
@@ -2038,8 +2038,7 @@ xcoff_end_psymtab (struct objfile *objfile, legacy_psymtab *pst,
       && pst->n_global_syms == 0
       && pst->n_static_syms == 0)
     {
-      /* Throw away this psymtab, it's empty.  We can't deallocate it, since
-         it is on the obstack, but we can forget to chain it on the list.  */
+      /* Throw away this psymtab, it's empty.  */
       /* Empty psymtabs happen as a result of header files which don't have
          any symbols in them.  There can be a lot of them.  */
 
-- 
2.17.2