Since the exposed API won't support config files:
- Don't use a config file for the demo app.
- Don't use config files for tests that don't need one.
Also, in preparation for removing command line argument support
entirely, remove all arguments from config files. Where we were using
arguments to specify behavior, use different binaries instead.
Tweak: Improve error reporting in the benchmark after I got a (sadly
non-reproducible) failure.
Bug: 250876593
Bug: 243513572
Test: atest MicrodroidTests MicrodroidHostTestCases
Test: atest MicrodroidBenchmarkApp
Test: manual - install & run demo app
Change-Id: I4332b2340bf2e18cdaee5acd9ef3277766b1c0b5