parse_remote_port: fix ;type= URL suffix over HTTP proxy

Test 563 is enabled now and verifies that the combo FTP type=A URL,
CURLOPT_PORT set and proxy work fine. As a bonus I managed to remove the
somewhat odd FTP check in parse_remote_port() and instead converted it
to a better and more generic 'slash_removed' struct field. Checking the
->protocol field isn't right since when an FTP:// URL is sent over a
HTTP proxy, the protocol is HTTP but the URL was handled by the FTP code
and thus slash_removed is set TRUE for this case.

tests/data/test563

@@ -47,7 +47,7 @@ ftp_proxy=http://%HOSTIP:%HTTPPORT/
 # Verify data after the test has been "shot"
 <verify>
 <protocol>
-GET ftp://%HOSTIP:%FTPPORT/563;type=A HTTP/1.1
+GET FTP://%HOSTIP:%FTPPORT/563;type=A HTTP/1.1
 Host: %HOSTIP:%FTPPORT
 Accept: */*
 Proxy-Connection: Keep-Alive