Re-enable minification to fix the doc build

Disable isn't possible for non-nightly versions of Rust, so this is
currently breaking the doc build. In addition, it seems that the
original issue that triggered this change [^1] is now fixed.

[^1]: rust-lang/rust#58849

Author: mrobinson

.github/workflows/docs.yml

@@ -23,7 +23,7 @@ jobs:
       - name: Compile docs
         run: python3 ./mach doc
         env:
-          RUSTDOCFLAGS: -Z unstable-options --disable-minification --document-private-items
+          RUSTDOCFLAGS: --document-private-items
       - name: Upload docs
         run: |
           cd target/doc