[issue37663] Making venv activation script prompts consistent

[Brett Cannon]

Change by Brett Cannon <brett at python.org>:


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dependencies: +Drop support for Aspen magic directories in venv's activate scripts, venv activation scripts erroneously check if __VENV_PROMPT__ is defined

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37663>
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