And finally remove the 'frames' property which was added for compatibility with 2.1
in bed3efb17e.
Fixes#21765.
The 'animations' property on the other hand is needed, contrarily to what its comment
said (copy-paste mistake probably).
Also removes unused '_get_animation_list'.
* Map is unnecessary and inefficient in almost every case.
* Replaced by the new HashMap.
* Renamed Map to RBMap and Set to RBSet for cases that still make sense
(order matters) but use is discouraged.
There were very few cases where replacing by HashMap was undesired because
keeping the key order was intended.
I tried to keep those (as RBMap) as much as possible, but might have missed
some. Review appreciated!
