ci: tox: fix py37-freeze
ci: tox: fix py37-freeze

Remove ``--no-use-pep517``, which appears to not be supported anymore,
and PyInstaller works without it by now.

The-Compiler/pytest,nicoddemus/pytest,Akasurde/pytest,tomviner/pytest,The-Compiler/pytest,RonnyPfannschmidt/pytest,tomviner/pytest,pytest-dev/pytest,alfredodeza/pytest,nicoddemus/pytest,markshao/pytest