Bug 1607470, unset __PYVENV_LAUNCHER__ for virtualenvs, r=firefox-bui…

…ld-system-reviewers,rstewart

The __PYVENV_LAUNCHER__ is set on macos to indicate which
python to use. Sadly, keeping this set confuses pip in
virtualenvs.
This corresponds to python/cpython#9516.

Differential Revision: https://phabricator.services.mozilla.com/D59853

UltraBlame original commit: ed91bca1f4a669454801390a1e5432fa2cd9561e

python/mozbuild/mozbuild/virtualenv.py

@@ -1539,6 +1539,47 @@
 "
 "
 
+#
+__PYVENV_LAUNCHER__
+confuses
+pip
+about
+the
+python
+interpreter
+
+#
+See
+https
+:
+/
+/
+bugzilla
+.
+mozilla
+.
+org
+/
+show_bug
+.
+cgi
+?
+id
+=
+1607470
+
+os
+.
+environ
+.
+pop
+(
+'
+__PYVENV_LAUNCHER__
+'
+None
+)
+
 if
 self
 .