Removes all legacy wallet specific functional tests.
Also removes the --descriptor and --legacy-wallet options as these are
no longer necessary with the legacy wallet removed.
Review note: The changes are complete, because self.options.descriptors
is set to None in parse_args (test_framework.py).
A value of None implies -disablewallet, see the previous commit.
So if a call to add_wallet_options is missing, it will lead to a test
failure when the wallet is compiled in.