[gdb/testsuite] Simplify gdb.dwarf2/locexpr-data-member-location.exp

When reverting commit 5a20fadc841 the test-case
gdb.dwarf2/locexpr-data-member-location.exp runs into an internal-error.

Simplify the test-case by triggering the internal-error using gdb_unload
instead of runto "bar".

Tested on x86_64-linux.

---
 gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp b/gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp
index 1f70e6a34bd..98f9270d7bb 100644
--- a/gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp
+++ b/gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp
@@ -40,7 +40,7 @@
 #    purging of shared objects.
 #
 # 3) After performing some simple gdb commands, the program is
-#    run again.  In the course of running the objfile destructor
+#    discarded.  In the course of running the objfile destructor
 #    associated with the shared object, values are preserved
 #    along with their types.  As noted earlier, it was during
 #    the recursive type copy that the bug was observed.
@@ -342,8 +342,7 @@ gdb_test "step" "bar \\(.*" "step into bar"
 
 # We don't want a clean restart here since that will be too clean.
 # The original reproducer for PR28030 set a breakpoint in the shared
-# library and then restarted via "run".  The command below does roughly
-# the same thing.  It's at this step that an internal error would
-# occur for PR28030.  The "message" argument tells runto to turn on
-# the printing of PASSes while runto is doing its job.
-runto "bar" message
+# library and then restarted via "run".  The command below is more minimal:
+# it discards executable file and symbol table.  It's at the latter step
+# that an internal error would occur for PR28030.
+gdb_unload