largefiles: register wire protocol commands with modern APIs The wireproto.wireprotocommand decorator is the preferred mechanism for registering wire protocol commands. In addition, wireproto.commands is no longer a 2-tuple and use of that 2-tuple API should be considered deprecated. This commit ports largefiles to use wireproto.wireprotocommand() and ports to the "commandentry" API. As part of this, the definition of the "lheads" wire protocol command is moved to the proper stanza. We stop short of actually using wireprotocommand as a decorator in order to minimize churn. We should ideally move wire protocol commands to the registrar mechanism. But that's for another changeset. Differential Revision: https://phab.mercurial-scm.org/D2018