transport: rename got_remote_heads

transport: rename got_remote_heads

The 'got_remote_heads' member of 'struct git_transport_data' was used
historically to indicate that the initial server connection was made and
the ref advertisement was returned. With protocol v2, that initial
handshake does not necessarily include the ref advertisement, so this
member is not an accurate name. Thankfully, all uses of the member are
only checking to see if the handshake should take place, not whether or
not some local data has the ref advertisement.

Rename the member to 'finished_handshake' to represent the proper state.
Note that the variable is only set to 1 during the handshake() method.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>