Merge bitcoin/bitcoin#31390: Remove src/config directory

935973b Remove `src/config` directory (Hennadii Stepanov)

Pull request description:

  The `src/config` directory has not been used since the migration to CMake, which disables in-source builds.

ACKs for top commit:
  TheCharlatan:
    ACK 935973b
  BrandonOdiwuor:
    ACK 935973b

Tree-SHA512: cc5b405e39387673fa2fd1e96680295b6eb3dc49a5f9a4d288580b8ea83efba04c96132811ca2cec14bcca509dbaf20c390cd47dabeea2a6ebc973e364e7a43b