chore: Remove Phemex from blocklist.

not providing history is not necessarily a reason to hard-block an exchange.

freqtrade/exchange/common.py

@@ -37,7 +37,6 @@ def _get_logging_mixin():
 
 BAD_EXCHANGES = {
     "bitmex": "Various reasons.",
-    "phemex": "Does not provide history.",
     "probit": "Requires additional, regular calls to `signIn()`.",
     "poloniex": "Does not provide fetch_order endpoint to fetch both open and closed orders.",
 }