GH-125722: Increase minimum supported Sphinx to 8.1.3 (#128922)

Doc/conf.py

@@ -9,9 +9,6 @@
 import importlib
 import os
 import sys
-import time
-
-import sphinx
 
 # Make our custom extensions available to Sphinx
 sys.path.append(os.path.abspath('tools/extensions'))
@@ -97,7 +94,8 @@ today_fmt = '%B %d, %Y'
 highlight_language = 'python3'
 
 # Minimum version of sphinx required
-needs_sphinx = '7.2.6'
+# Keep this version in sync with ``Doc/requirements.txt``.
+needs_sphinx = '8.1.3'
 
 # Create table of contents entries for domain objects (e.g. functions, classes,
 # attributes, etc.). Default is True.
@@ -376,13 +374,7 @@ html_context = {
 
 # This 'Last updated on:' timestamp is inserted at the bottom of every page.
 html_last_updated_fmt = '%b %d, %Y (%H:%M UTC)'
-if sphinx.version_info[:2] >= (8, 1):
-    html_last_updated_use_utc = True
-else:
-    html_time = int(os.environ.get('SOURCE_DATE_EPOCH', time.time()))
-    html_last_updated_fmt = time.strftime(
-        html_last_updated_fmt, time.gmtime(html_time)
-    )
+html_last_updated_use_utc = True
 
 # Path to find HTML templates to override theme
 templates_path = ['tools/templates']
@@ -619,16 +611,6 @@ extlinks = {
 }
 extlinks_detect_hardcoded_links = True
 
-if sphinx.version_info[:2] < (8, 1):
-    # Sphinx 8.1 has in-built CVE and CWE roles.
-    extlinks |= {
-        "cve": (
-            "https://www.cve.org/CVERecord?id=CVE-%s",
-            "CVE-%s",
-        ),
-        "cwe": ("https://cwe.mitre.org/data/definitions/%s.html", "CWE-%s"),
-    }
-
 # Options for c_annotations extension
 # -----------------------------------