Fix flakiness in TrustedPresenationCallback tests

On certain devices, these tests can fail since they are expecting all
pixels in the SC to be visible. Some configurations show content above
the SC content that can't be prevented. Instead, drop the threshold
since it doesn't need to be 100% visible to test
TrustedPresentationCallback.

Test: TrustedPresentationCallbackTest
Bug: 279957280
Bug: 281946355
(cherry picked from commit d8bbfe27ac2471d31a59123215945940974fca60)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:2ec17a5ef0d29af4b6ddc6a212caefc22ecbce58)
Merged-In: I4709115278135bde463eb4ed2de250f5041ea3e3
Change-Id: I4709115278135bde463eb4ed2de250f5041ea3e3