gh-36959: `.devcontainer/downstream-archlinux-latest`: Fix maxima
    
Dev container configurations `.devcontainer/downstream-*` give easy
access to Sage as provided by downstream packagers (see https://doc.sage
math.org/html/en/developer/portability_testing.html#using-our-pre-built-
docker-images-for-development-in-vs-code, bottom).

Unfortunately maxima is defective when the archlinux sage package is
installed in the official archlinux Docker container because of
NoExtract directives that make the maxima help system inoperable.

Here we apply the same fix that we used in #36391 for the portability
CI: Removing the NoExtract directives before installing the package.

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URL: #36959
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee

Author: Release Manager

.devcontainer/downstream-archlinux-latest/devcontainer.json

@@ -3,7 +3,7 @@
     "name": "archlinux:latest downstream Sage",
     "image": "archlinux:latest",
     // Create an empty bashrc to avoid the error "No such file or directory" when opening a terminal.
-    "onCreateCommand": "EXTRA_SYSTEM_PACKAGES='sagemath sagemath-doc' EXTRA_SAGE_PACKAGES='notebook pip' .devcontainer/onCreate.sh && touch ~/.bashrc",
+    "onCreateCommand": "sed -i '/^NoExtract/d' /etc/pacman.conf; EXTRA_SYSTEM_PACKAGES='sagemath sagemath-doc' EXTRA_SAGE_PACKAGES='notebook pip' .devcontainer/onCreate.sh && touch ~/.bashrc",
     // There's no SAGE_LOCAL, so remove the symlink 'prefix'.
     "updateContentCommand": "rm -f prefix && ln -sf /usr venv",
     "extensions": [