derivation-ok-restriction.2 (a base required attribute may not become
optional in a restriction) ran only over complexContent restrictions, so
a simpleContent restriction that relaxed a required attribute was accepted.
The attribute-use restriction check now runs over both derivation roots.
Closes XSTS particlesZ030_d, which libxml2 also rejects, so this aligns
with the reference rather than exceeding it. XSTS invalid-schemas-accepted
10 to 9 with valid-schemas-rejected held at 0 (full archive). Guarded by
SimpleContentAttrRestrictionTests; the XSTSSuiteTests baseline is updated.