Remove build requirements from building arm

The meson build switched to generating the file grammars and using meson
to build the manpages/ARM. This is because meson doesn't work well when
writing files outside the build directory.

However, this has been suboptimal when someone only wants to build the
documentation (like RTD). Sphinx can now be used outside meson like it
was with autoconf.

Grammars are now updated by the developer with CI checking if one is
needed or not, like clang-format.

doc/arm/conf.py

@@ -11,8 +11,8 @@
 # information regarding copyright ownership.
 ############################################################################
 
-import os
 import sys
+import re
 
 from pathlib import Path
 from typing import List, Tuple
@@ -151,7 +151,15 @@ project = "BIND 9"
 copyright = "2023, Internet Systems Consortium"
 author = "Internet Systems Consortium"
 
-version = os.getenv("BIND_PROJECT_VERSION")
+meson_path = Path(__file__).resolve().parent.parent.parent / "meson.build"
+with meson_path.open(encoding="utf-8") as meson_build:
+    pattern = re.compile(r"    version: '(?P<version>.*)',")
+    for line in meson_build:
+        match = pattern.match(line)
+        if match:
+            version = match.group("version")
+            assert version.startswith("9.")
+            break
 
 release = version