style: enforce short array syntax via StyleCI

Removes long_array_syntax from the disabled rules so StyleCI enforces
the short syntax this PR converts the codebase to.

.styleci.yml

@@ -17,7 +17,6 @@ disabled:
   - concat_without_spaces
   - declare_equal_normalize
   - heredoc_to_nowdoc
-  - long_array_syntax
   - method_argument_space_strict
   - new_with_braces
   - no_alternative_syntax