Remove composer.json file requirement

This is because we can't be sure which arguments require a json file
and which don't, so the `else' statement will always be difficult to
check for correctness.

plugins/composer/composer.plugin.zsh

@@ -20,18 +20,15 @@ _composer () {
   _arguments \
     '1: :->command'\
     '*: :->args'
-  if [ -f composer.json ]; then
+
   case $state in
     command)
-        compadd `_composer_get_command_list`
+      compadd $(_composer_get_command_list)
       ;;
     *)
-        compadd `_composer_get_required_list`
+      compadd $(_composer_get_required_list)
       ;;
   esac
-  else
-    compadd create-project init search selfupdate show
-  fi
 }
 
 compdef _composer composer