Merge pull request #1314 from tbetbetbe/grpc_ruby_remove_xray_dep

src/ruby/grpc.gemspec

src/ruby/lib/grpc/generic/client_stub.rb

src/ruby/lib/grpc/generic/rpc_server.rb

src/ruby/spec/generic/client_stub_spec.rb

src/ruby/spec/generic/rpc_server_pool_spec.rb

src/ruby/spec/generic/rpc_server_spec.rb