gdb/dwarf: remove unnecessary local variable in dw2_get_file_names_reader

It seems like the lh_cu variable is not necessary, we can just use
this_cu.

Change-Id: Ic2ed6ee82faf1fb5d340cd92dc8ef15434b20cb8
Approved-By: Tom Tromey <tom@tromey.com>
1 file changed