refactor(go)!: remove deprecated `go` plugin

BREAKING CHANGE: the `go` plugin has been removed. Use the `golang` plugin instead.

plugins/go/README.md

-The go plugin is deprecated. Use the [golang plugin](https://github.com/ohmyzsh/ohmyzsh/tree/master/plugins/golang) instead.

plugins/go/go.plugin.zsh

-print -P "%F{yellow}The 'go' plugin is deprecated. Use the '%Ugolang%u' plugin instead.%f"
-
-source "$ZSH/plugins/golang/golang.plugin.zsh"