Remove ss_event and the C resolver shim

Each program's loop, signals, plugin watcher and stats timer now go
through ss::event::Program (src/event/program.hpp), held on main()'s
stack; ss-manager uses it too. ss-server resolves the manager address
with the relay resolver. With no C caller left, ss_event.cpp/.h,
resolv.cpp/.h and their C tests go; test_resolver_cpp.cpp replaces the
resolver tests against the same delayed local DNS server, and ss_ev is
now an interface target over libuv.

scripts/no_heap_baseline.txt

@@ -15,8 +15,7 @@ src/plugin.cpp 3
 src/process.cpp 26
 src/redir.cpp 1
 src/rule.cpp 2
-src/server.cpp 4
-src/ss_event.cpp 5
+src/server.cpp 3
 src/ssurl.cpp 3
 src/stream.cpp 3
 src/tunnel.cpp 1