Redefine macro checks for reflections

Now that we define the macro on the reflection type we no longer
need to check `macro == :what` on each type for `belongs_to?` or
`has_one?` etc. These now default to false unless it's defined
in the reflection class.

Reuse existing belongs_to? method to check macros

We don't need to do `:belongs_to == macro` anymore becasue we
have a `belongs_to?` method. I didn't find this being used
anywhere for `has_one?` or `collection?` since they were already
fixed.
Merge pull request #16351 from eileencodes/finish-refactoring-macro-to-eliminate-checking-against-symbols

Redefine macro checks for reflections