linter: Remove deprecated NodeLintRegistry.addOnClause

Cq-Include-Trybots: luci.dart.try:flutter-analyze-try,analyzer-win-release-try,pkg-win-release-try
Change-Id: I3c1b1ee14591b21c9ea718178e0650a84bf51d95
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/366404
Auto-Submit: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Commit-Queue: Phil Quitslund <pquitslund@google.com>

pkg/analyzer/lib/src/lint/linter_visitor.dart

@@ -701,8 +701,8 @@ class LinterVisitor implements AstVisitor<void> {
     node.visitChildren(this);
   }
 
-  @Deprecated('Use visitMixinOnClause() instead')
   @override
+  // ignore: deprecated_member_use_from_same_package
   void visitOnClause(OnClause node) {
     _runSubscriptions(node, registry._forMixinOnClause);
     node.visitChildren(this);
@@ -1815,11 +1815,6 @@ class NodeLintRegistry {
     _forObjectPattern.add(_Subscription(linter, visitor, _getTimer(linter)));
   }
 
-  @Deprecated('Use addMixinOnClause() instead')
-  void addOnClause(LintRule linter, AstVisitor visitor) {
-    addMixinOnClause(linter, visitor);
-  }
-
   void addParenthesizedExpression(LintRule linter, AstVisitor visitor) {
     _forParenthesizedExpression
         .add(_Subscription(linter, visitor, _getTimer(linter)));