tox: remove basepython = python3 lines

I don't think they're needed.

Author: bluetech

tox.ini

@@ -100,7 +100,6 @@ wheel_build_env = .pkg
 description =
     run pre-commit-defined linters under `{basepython}`
 skip_install = True
-basepython = python3
 deps = pre-commit>=2.9.3
 commands = pre-commit run --all-files --show-diff-on-failure {posargs:}
 setenv =
@@ -128,7 +127,6 @@ setenv =
 [testenv:docs-checklinks]
 description =
     check the links in the documentation with `{basepython}`
-basepython = python3
 usedevelop = True
 changedir = doc/en
 deps = -r{toxinidir}/doc/en/requirements.txt
@@ -142,7 +140,6 @@ setenv =
 description =
     regenerate documentation examples under `{basepython}`
 changedir = doc/en
-basepython = python3
 passenv =
     SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYTEST
 deps =
@@ -195,7 +192,6 @@ commands =
 
 [testenv:release]
 description = do a release, required posarg of the version number
-basepython = python3
 usedevelop = True
 passenv = *
 deps =
@@ -213,7 +209,6 @@ commands = python scripts/prepare-release-pr.py {posargs}
 
 [testenv:generate-gh-release-notes]
 description = generate release notes that can be published as GitHub Release
-basepython = python3
 usedevelop = True
 deps =
     pypandoc