[gdb/testsuite] Fix gdb.dwarf2/forward-spec.exp with read1

When running test-case gdb.dwarf2/forward-spec.exp with check-read1 we run
into:
...
    parent:     ((cooked_index_entry *) 0xFAIL: <exp>: v has a parent
7fdc1c002ed0) [ns]^M
...

The problem is using regexps containing '.' to avoid escaping, which makes
them too generic.

Fix this by eliminating the '.' from the regexps.

Tested on x86_64-linux.