The traditional multisig workflow doesn't work with descriptor wallets
so make these tests legacy wallet only.
This is a backport of core#18788 [9/15]
https://github.com/bitcoin/bitcoin/pull/18788/commits/47d3243160fdec7e464cfb8f869be7f5d4ee25fe
Notes for reviewers:
- the sanity checks introduced in D2546 belong to the indented code, so I had to move them up (move & indent only)
- the "RAW TX MULTISIG TESTS 2of2 tests" are indented only. The only changes are code formatting to keep lines below 80 characters.