transport-helper: no connection restriction in connect_helper

When commit b236752 (Support remote archive from all smart transports,
2009-12-09) added "remote archive" support for "smart transports", it
was for transport that supports the ".connect" method. The
"connect_helper()" function protected itself from getting called for a
transport without the method before calling process_connect_service(),
which only worked with the ".connect" method.

Later, commit edc9caf (transport-helper: introduce stateless-connect,
2018-03-15) added a way for a transport without the ".connect" method
to establish a "stateless" connection in protocol v2, where
process_connect_service() was taught to handle the ".stateless_connect"
method, making the old protection too strict. But commit edc9caf forgot
to adjust this protection accordingly. Even at the time of commit
b236752, this protection seemed redundant, since
process_connect_service() would return 0 if the connection could not be
established, and connect_helper() would still die() early.

Remove the restriction in connect_helper() and give the function
process_connect_service() the opportunity to establish a connection
using ".connect" or ".stateless_connect" for protocol v2. So we can
connect with a stateless-rpc and do something useful. E.g., in a later
commit, implements remote archive for a repository over HTTP protocol.

Helped-by: Junio C Hamano <[email protected]>
Helped-by: Linus Arver <[email protected]>
Signed-off-by: Jiang Xin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jiangxin

transport-helper.c

@@ -662,8 +662,6 @@ static int connect_helper(struct transport *transport, const char *name,
 
 	/* Get_helper so connect is inited. */
 	get_helper(transport);
-	if (!data->connect)
-		die(_("operation not supported by protocol"));
 
 	if (!process_connect_service(transport, name, exec))
 		die(_("can't connect to subservice %s"), name);