mv "electrum seed" stuff from bitcoin.py to mnemonic.py

electrum/old_mnemonic.py

@@ -1652,13 +1652,13 @@ words = [
 "total",
 "unseen",
 "weapon",
-"weary"
+"weary",
 ]
 
+n = len(words)
+assert n == 1626
 
 
-n = 1626
-
 # Note about US patent no 5892470: Here each word does not represent a given digit.
 # Instead, the digit represented by a word is variable, it depends on the previous word.