[gdb/testsuite] Clean up redundant info in gdb.dwarf2

[gdb/testsuite] Clean up redundant info in gdb.dwarf2

In gdb.dwarf2/ada-valprint-error.exp we find:
...
    untested ${testfile}.exp
...
such that we have:
...
UNTESTED: gdb.dwarf2/ada-valprint-error.exp: ada-valprint-error.exp
...

Fix this and a likewise unsupported message in
gdb.dwarf2/dw2-dir-file-name.exp.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-10-20  Tom de Vries  <tdevries@suse.de>

	* gdb.dwarf2/ada-valprint-error.exp: Remove redundant mention of .exp
	file.
	* gdb.dwarf2/dw2-dir-file-name.exp: Same.