CI: Drop usage of nix-build-uncached

We're not caching anything at the moment anymore... so it became
redundant.

It also is explicitly made to only work with Nix.
It does not work with Lix.

Additionally, this has been deprecated and replaced by another tool,
which does not even support passing attributes.

.github/workflows/build.yml

@@ -32,9 +32,4 @@ jobs:
       - name: Install Lix
         uses: samueldr/lix-gha-installer-action@v1
 
-      - name: Install nix-build-uncached
-        # Save evaluation time by pulling directly from cache.nixos.org
-        # nixpkgs rev 12303c652b881435065a98729eb7278313041e49
-        run: nix-env -i /nix/store/npzpwxjbxlgbi0kfji2x44nssksxk4zw-nix-build-uncached-1.1.2
-
-      - run: nix-build-uncached .ci/get-flake.nix -A "${{ matrix.attr }}"
+      - run: nix-build .ci/get-flake.nix -A "${{ matrix.attr }}"