fix(nix): remove stale packages/shared filter

The filter for packages/shared has been inert since the rename to
packages/core (#24309). Nix builds pass without it — core deps are
resolved via hoisting from packages/opencode.

Fixes #24929

Author: jerome-benoit

nix/node_modules.nix

@@ -55,7 +55,6 @@ stdenvNoCC.mkDerivation {
       --filter './packages/opencode' \
       --filter './packages/desktop' \
       --filter './packages/app' \
-      --filter './packages/shared' \
       --frozen-lockfile \
       --ignore-scripts \
       --no-progress