refactor(zsh_reload)!: remove deprecated plugin

BREAKING CHANGE: the `zsh_reload` was deprecated long ago and showed
a deprecation message. The `src` function was replaced by the CLI
command `omz reload`, so use that instead from now on.

plugins/zsh_reload/README.md

-# zsh_reload plugin
-
-**This plugin is deprecated.** Use `omz reload` or `exec zsh` instead.

plugins/zsh_reload/zsh_reload.plugin.zsh

-print ${(%):-"%F{yellow}The \`zsh_reload\` plugin is deprecated and will be removed."}
-print ${(%):-"Use \`%Bomz reload%b\` or \`%Bexec zsh%b\` instead.%f"}
-
-src() {
-  print ${(%):-"%F{yellow}$0 is deprecated. Use \`%Bomz reload%b\` or \`%Bexec zsh%b\` instead.%f\n"}
-  omz reload
-}