removes cached pixelbufferpool and instead retrieves current pool from the compressionSession each time (as recommended by apple docs) Bug: webrtc:14688 Change-Id: I2244e69e7f32b912021db0905b9d5867d0bf6357 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/284240 Reviewed-by: Kári Helgason <kthelgason@webrtc.org> Commit-Queue: Kári Helgason <kthelgason@webrtc.org> Cr-Commit-Position: refs/heads/main@{#38920}