tests: Using manual elements instead of autotools elements where possible

Affected tests:

  - _testing/_sourcetests/project (standard source tests)
  - tests/frontend/exceptions
  - tests/frontend/completions.py
  - tests/frontend/project/elements/multiple_targets
  - tests/format/dependencies.py
  - tests/format/assertion.py
  - tests/format/option-overrides
  - tests/format/optionarch.py
  - tests/format/optionbool.py
  - tests/format/optioneltmask.py
  - tests/format/optionflags.py
  - tests/format/optionos.py
  - tests/format/optionexports.py
  - tests/format/optionenum.py
  - tests/format/options.py
  - tests/format/listdirectiveerrors.py
  - tests/format/project.py
  - tests/sourcecache/config.py
  - tests/artifactcache/config.py
  - tests/sources/tar.py
  - tests/sources/remote.py
  - tests/sandboxes/remote-exec-config.py
107 files changed