rename key2file and file2key

What these generate is not really suitable to be used as a filename,
which is why keyFile and fileKey further escape it. These are just
serializing Keys.

Also removed a quickcheck test that was very unlikely to test anything
useful, since it relied on random chance creating something that looks
like a serialized key. The other test is sufficient for testing what
that was intended to test anyway.

Command/TransferKeys.hs

@@ -126,5 +126,5 @@ instance TCSerialized RemoteName where
 	deserialize n = Just n
 
 instance TCSerialized Key where
-	serialize = key2file
-	deserialize = file2key
+	serialize = serializeKey
+	deserialize = deserializeKey