gnu: python-asgiref: Do not set PYTHONPATH.

* gnu/packages/python-web.scm (python-asgiref)
[phases]{check}: Do not set PYTHONPATH.

gnu/packages/python-web.scm

@@ -247,9 +247,6 @@ comes with a SOCKS proxy client.")
      '(#:phases (modify-phases %standard-phases
                   (replace 'check
                     (lambda _
-                      (setenv "PYTHONPATH"
-                              (string-append "./build/lib:"
-                                             (getenv "PYTHONPATH")))
                       (invoke "pytest" "-vv"))))))
     (native-inputs
      `(("python-pytest" ,python-pytest)