Remove dependence on SkTRegistry

Test: Existing CTS tests for Movie.

SkTRegistry was renamed and moved (with the intent of being private to
Skia) in https://skia-review.googlesource.com/c/6881.

There is only one class registred anyway, so make Movie::DecodeStream
just check GIF manually.

Change-Id: I7fa668cf13c902b49f2848bce4d86ad83020970f