MINOR: http-rule/tcp-rules: Make track-sc* custom actions

MINOR: http-rule/tcp-rules: Make track-sc* custom actions

Now, these actions use their own dedicated function and are no longer handled
"in place" during the TCP/HTTP rules evaluation. Thus the action names
ACT_ACTION_TRK_SC0 and ACT_ACTION_TRK_SCMAX are removed. The action type is now
the tracking index. Thus the function trk_idx() is no longer needed.