Exchanges/OTC section cleanup

[peterzen]

• Binance OTC doesn't do DCR, maybe it can be removed from the OTC section.
• https://reciprocitytrading.com/ is dead
• Escher seems like it's a platform for OTC dealers rather than an OTC service itself

[johncodesit]

@peterzen Hi! I'm new to decred, looking for some first good issue to start contributing to the project. Do you believe this is a good starting point? If not, where could I help? Thanks in advance

[jzbz]

@peterzen Binance OTC doesn't seem to actually do OTC any longer and Reciprocity was acquired, they can both be removed.
Escher (formerly i2) still trades OTC, my understanding is that clients onboard thorough the app now, so we should leave that one.

[jholdstock]

@johncodesit feel free to implement the suggestions from @jzbz

[exitus1]

It looks like Decred is no longer on Exchange Transak: https://global.transak.com/

[jzbz]

Pinging them to see what's up.

[jzbz]

This can be closed, addressed here: #983