_asciidoc_fallback_path: Remove reading from parent directories

Reading paths from outside the Python package worked in pkg_resources < 40.8.0
but got deprecated afterwards: https://github.com/pypa/setuptools/pull/1640

Since this isn't really any critical functionality, let's just not try reading
from there. We can still revisit this when the switch to Sphinx is complete.

Fixes #4576 (hopefully)
See #345

qutebrowser/browser/qutescheme.py

@@ -32,7 +32,6 @@ import textwrap
 import urllib
 import collections
 import base64
-import os.path
 
 try:
     import secrets
@@ -342,17 +341,9 @@ def qute_gpl(_url):
 def _asciidoc_fallback_path(html_path):
     """Fall back to plaintext asciidoc if the HTML is unavailable."""
     asciidoc_path = html_path.replace('.html', '.asciidoc')
-    asciidoc_paths = [asciidoc_path]
-    if asciidoc_path.startswith('html/doc/'):
-        asciidoc_paths += [asciidoc_path.replace('html/doc/', '../doc/help/'),
-                           asciidoc_path.replace('html/doc/', '../doc/')]
-
-    for path in asciidoc_paths:
     try:
-            return utils.read_file(os.path.normpath(path))
+        return utils.read_file(path)
     except OSError:
-            pass
-
         return None