runtime: remove unused enum maxround
runtime: remove unused enum maxround

LGTM=minux, dave
R=golang-codereviews, minux, dave
CC=golang-codereviews
https://codereview.appspot.com/122030043

bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,webfd/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,webfd/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,webfd/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc