Merge rust-bitcoin/rust-bitcoin#871: Delete contract hash module

7f33fe6 Delete contract hash module (Tobin Harding)

Pull request description:

  This module has been deprecated in commit 1ffdce9 in August 2020, it is safe to delete it now.

  Fixes: #322

ACKs for top commit:
  apoelstra:
    ACK 7f33fe6
  Kixunil:
    ACK 7f33fe6
  dr-orlovsky:
    ACK 7f33fe6

Tree-SHA512: f218c8b0c09b14cd885cd7cf03c0a4623e5ead785decbc62a2f9610d438d5ea3efd2e2b47172a7608e33714996efa121707583d4257fa683dbfc9717988ceda6

Author: apoelstra