refactor(plugins): remove old generated completion files

This removes .gitignore plugin files and adds a force-rm of the old completion file,
which ignores any errors if the file doesn't exist.

plugins/deno/deno.plugin.zsh

@@ -12,6 +12,9 @@ alias dup='deno upgrade'
 
 # COMPLETION FUNCTION
 if (( $+commands[deno] )); then
+  # remove old generated completion file
+  command rm -f "${0:A:h}/_deno"
+
   ver="$(deno --version)"
   ver_file="$ZSH_CACHE_DIR/deno_version"
   comp_file="$ZSH_CACHE_DIR/completions/_deno"