remove unused errors in checkGrammarModifiers (#47198)

Author: romdotdog

src/compiler/checker.ts

@@ -42583,7 +42583,7 @@ namespace ts {
                 return quickResult;
             }
 
-            let lastStatic: Node | undefined, lastDeclare: Node | undefined, lastAsync: Node | undefined, lastReadonly: Node | undefined, lastOverride: Node | undefined;
+            let lastStatic: Node | undefined, lastDeclare: Node | undefined, lastAsync: Node | undefined, lastOverride: Node | undefined;
             let flags = ModifierFlags.None;
             for (const modifier of node.modifiers!) {
                 if (modifier.kind !== SyntaxKind.ReadonlyKeyword) {
@@ -42690,7 +42690,6 @@ namespace ts {
                             return grammarErrorOnNode(modifier, Diagnostics.readonly_modifier_can_only_appear_on_a_property_declaration_or_index_signature);
                         }
                         flags |= ModifierFlags.Readonly;
-                        lastReadonly = modifier;
                         break;
 
                     case SyntaxKind.ExportKeyword:
@@ -42809,18 +42808,12 @@ namespace ts {
                 if (flags & ModifierFlags.Static) {
                     return grammarErrorOnNode(lastStatic!, Diagnostics._0_modifier_cannot_appear_on_a_constructor_declaration, "static");
                 }
-                if (flags & ModifierFlags.Abstract) {
-                    return grammarErrorOnNode(lastStatic!, Diagnostics._0_modifier_cannot_appear_on_a_constructor_declaration, "abstract"); // TODO: GH#18217
-                }
                 if (flags & ModifierFlags.Override) {
                     return grammarErrorOnNode(lastOverride!, Diagnostics._0_modifier_cannot_appear_on_a_constructor_declaration, "override"); // TODO: GH#18217
                 }
-                else if (flags & ModifierFlags.Async) {
+                if (flags & ModifierFlags.Async) {
                     return grammarErrorOnNode(lastAsync!, Diagnostics._0_modifier_cannot_appear_on_a_constructor_declaration, "async");
                 }
-                else if (flags & ModifierFlags.Readonly) {
-                    return grammarErrorOnNode(lastReadonly!, Diagnostics._0_modifier_cannot_appear_on_a_constructor_declaration, "readonly");
-                }
                 return false;
             }
             else if ((node.kind === SyntaxKind.ImportDeclaration || node.kind === SyntaxKind.ImportEqualsDeclaration) && flags & ModifierFlags.Ambient) {