wireproto: avoid exposing pushkey abort for server without evolution Client with evolution enabled will query the 'obsolete' pushley namespace if no other way to request obsmarkers have been found. They will do this unconditionally as long as no other obsolescence related capabilities have been advertised by the server. The call is "harmless" since the namespace will be empty if obsmarkers exchange is disabled. However, since we forbid the use of pushkey for obsmarkers this lead to unexpected crash report for up to date client talking to a server with the evolve extensions but exchange disabled. We fix the issue by serving the expected empty namespace in this case. We keep forbidding the query if obsmarker exchange is enabled since new client should have picked another more effective was to fetch the data first. We also add some tests for this logic.