feat(destinations): the post-16 section, replacing the placeholder

The 'Post-16 destination data coming soon' note is deleted rather than
reworded: for a school with no sixth form the truthful statement is that
the question does not apply, and a placeholder there implies something is
missing. hasSixthForm and .sixthFormNote go with it — nothing else used them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BvdDKvFFSZuMVDH5fEyTob

nextjs-app/components/school/schoolSections.module.css

@@ -1883,15 +1883,7 @@
     color: var(--phase-secondary-text);
     border: 1px solid rgba(var(--status-above-rgb), 0.2);
 }
-.sixthFormNote {
-    margin-top: 1rem;
-    padding: 0.625rem 0.875rem;
-    background: var(--bg-secondary);
-    border-radius: 6px;
-    font-size: 0.825rem;
-    color: var(--text-secondary);
-    border-left: 3px solid var(--brand);
-}
+
 .genderSplitHint {
     font-size: 0.7rem;
     color: var(--text-muted);
@@ -2107,7 +2099,6 @@
     border-top: 1px solid var(--border);
 }
 
-
 .cutoffMapFigure {
     /* Enough to read a set of concentric rings and no more — this is a
        diagram of a number, not a map anyone navigates by. */