[infra] Remove some unused files

The information in these files is now in the test_matrix.json instead.

Change-Id: I5ab3d038155c3201f564822bd4b6f23fdeb45307
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/150741
Auto-Submit: Alexander Thomas <athom@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>
Commit-Queue: William Hesse <whesse@google.com>
Reviewed-by: William Hesse <whesse@google.com>

Author: athomas