Removes the "Other Implementations" section, same rationale as #1576.
Since one of the reference implementation links is dead, I've also removed that.
ACK a26656133b3ba67bf5073132ab47a357a4ddc9fc
ACK a26656133b3ba67bf5073132ab47a357a4ddc9fc
Great idea
The BIP author doesn't appear to be active. Happy to revert the first commit if the BIP author so requests.