Remove always true 'cur_key is None' test in KeyData.read_from_gpg()

Since the pub: + fpr: sequence always appear in that order, once and on
top of a gpg with-colons output, the condition will always be true.

debexpo/tools/gnupg.py

@@ -290,7 +290,6 @@ class KeyData():
                 # Correlate fpr with the previous pub record, and start
                 # gathering information for a new key
                 if pub:
-                    if cur_key is None:
                     keys[fpr] = cur_key = cls(fpr, pub)
                     pub_fpr = fpr
                     pub = None