Remove `force_is_boundary` from Reverb add trajectory observer.
Remove `force_is_boundary` from Reverb add trajectory observer.

It also set the default priority to `1` in both Reverb observers.

PiperOrigin-RevId: 324251882
Change-Id: Ib6df541c0be0beb247b4794e1e329d8ac3a98371

tensorflow/agents,tensorflow/agents