This reverts commit 79759fea, reversing
changes made to dc36f4df.

Changes required to make build possible: create separate grpc++_base{,_unsecure}, move grpc_compression_trace definition, and remove an assertion about library initialization from server

Also add some missing rules in test/core/slice/BUILD.

Compilation fails on FreeBSD because not all POSIX
compliant systems end up including AF_INET from
other header files transitively.

AF_INET and AF_INET6 should be provided by
<sys/socket.h>.

Fix bins/opt/end2end_test --gtest_filter=ProxyEnd2end/ProxyEnd2endTest.RpcDeadlineExpires/1 GRPC_POLL_STRATEGY=poll

keys and values.

Since

    #...
    class Service:

    class NextService:
    #...

without a body or `pass` under `Service` is invalid
Python, we ensure a `pass` statement is always
emitted to make the generated code valid.