exchange: access requirements on repo instead of peer As part of formalizing the peer interface, I audited for attribute accesses for non-internal names to find API violations. This uncovered the code changed in this commit. localpeer.requirements is just an alias to the repo's requirements attribute. So, change the code to get the data from the source instead of relying on a one-off attribute in the localpeer type. Differential Revision: https://phab.mercurial-scm.org/D265