dh-virtualenv causes build path to be captured

[legoktm]

Was trying to reproduce securedrop-client and hit:

│ │ ├── ./opt/venvs/securedrop-client/bin/activate.xsh
│ │ │ @@ -24,15 +24,15 @@
│ │ │          del aliases["deactivate"]
│ │ │  
│ │ │  
│ │ │  # unset irrelevant variables
│ │ │  _deactivate(["nondestructive"])
│ │ │  aliases["deactivate"] = _deactivate
│ │ │  
│ │ │ -$VIRTUAL_ENV = r"/home/user/securedrop-builder/build/debbuild/packaging/securedrop-client/debian/securedrop-client/opt/venvs/securedrop-client"
│ │ │ +$VIRTUAL_ENV = r"/src/build/debbuild/packaging/securedrop-client/debian/securedrop-client/opt/venvs/securedrop-client"
│ │ │  
│ │ │  $_OLD_VIRTUAL_PATH = $PATH
│ │ │  $PATH = $PATH[:]
│ │ │  $PATH.add($VIRTUAL_ENV + _get_sep() + "bin", front=True, replace=True)
│ │ │  
│ │ │  if ${...}.get("PYTHONHOME", ""):
│ │ │      # unset PYTHONHOME if set

dh-virtualenv is supposed to patch out the build path, but it misses this file. I had previously pointed this out at freedomofpress/securedrop#6538 (comment) but filing it as an independent issue since it is affecting reproducibility.

[legoktm]

dh-virtualenv was dropped in freedomofpress/securedrop-client#1741.