gdb/dwarf: remove cutu_reader::read_cutu_die_from_dwo abbrev table parameter

This parameter is always used to set cutu_reader::m_dwo_abbrev_table.
Remove the parameter, and have read_cutu_die_from_dwo set the field
directly.

Change-Id: I6c0c7d23591fb2c3d28cdea1befa4e6b379fd0d3
Approved-By: Tom Tromey <tom@tromey.com>