In the following CL we are removing the use of axs_testing.js from browser_tests:
https://chromium-review.googlesource.com/c/chromium/src/+/894146
It was not being used there anyway, and is being replaced by axe-core.

However, axs_testing.js exists in at least one other place in the library, under infra/

We need to:
- remove references from everywhere that it is no longer needed
- remove the actual libraries (not sure if just the one under accessibility-audit can be removed, or the ones under infra/)
- replace with equivalent functionality (probably from axs-core)