wallet: Remove path checking code from createwallet RPC

Summary:
This commit does not change behavior except for error messages which now
include more complete information.

This is a backport of core#19619 [7/8]
https://github.com/bitcoin/bitcoin/pull/19619/commits/77d5bb72b8722ec7a6c7c33479a532cbd5870ba4

Depends on D10229

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10230