Blender Git Loki

VSE: Remove seq->tmp usage from transform code

This field was used for extend feature to get handle position of
metastrip children. Since D9972 extend feature works only on meta
strip itself, not it's children.
So `SEQ_transform_get_left_handle_frame()` second argument is always
false and can be removed.

Another instance of `seq->tmp usage` is hack to distinguish strips to be
shuffled, which is not covered by this patch.

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D10321