tests: Remove 'test_build' from the testlib

These gem5 builds are compiled automatically if required by a test.
Additionally, they are redundant given the existance of the compiler
tests, run daily.

Change-Id: I71141f82a86538a77384e684b9d261794e103b99
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63334
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
1 file changed