Remove tox from various scripts

[JennyPng]

Related to #42858

• removing mentions of tox across code and variable names
• continuation of work in Update docs and instructions to use azpysdk instead of tox #45480 , which mainly removes mentions of tox in docs and instructions files, and removes unused ymls

usages of tox to address:

• delete tox_harness.py
• delete dispatch_tox.py
• delete invoke-tox-parallel.ps1
• rename 'tox' mentioning vars in set_checks.py
• rename ToxTestEnv CI parameter across yml files, related to ^
• update environment_exclusions.py
• update package_utils.py invocation of breaking
• other misc. mentions of tox in code comments, etc.

todo maybe in a separate PR

• rename TOX_PIP_IMPL ?
• remove tox invocation from cosmos-staging.yml
  • remove tox from ci_tools.txt
  • remove tox from regression_tools.txt
• rename ToxEnvParallel
• mentions of tox under extend_skip_glob in 3 pyproject.tomls
• remove unnecessary uses of TOX_PIP_IMPL (setting to uv when invoking azpysdk in CI yml files)