Remove default-equivalent EXPECT_CALL from transceiver tests

The mock senders and receivers are NiceMock, so calls that return
defaults and aren't critical for the correctness of the test shouldn't
have EXPECT_CALL on them.

Drive-by fix while working on associated bug.

Bug: webrtc:439514253
Change-Id: Ide27eb61e51c16a20c535c9aa802db6dc5e241c4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/417620
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Auto-Submit: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#45951}