remove useless condition as argumentExpression is always defined (microsoft#31567)

* remove useless condition as argumentExpression is always defined

* fix formatting

* remove obsolete diagnostic

Author: ajafff

src/compiler/binder.ts

@@ -778,7 +778,7 @@ namespace ts {
         function isNarrowableReference(expr: Expression): boolean {
             return expr.kind === SyntaxKind.Identifier || expr.kind === SyntaxKind.ThisKeyword || expr.kind === SyntaxKind.SuperKeyword ||
                 (isPropertyAccessExpression(expr) || isNonNullExpression(expr) || isParenthesizedExpression(expr)) && isNarrowableReference(expr.expression) ||
-                isElementAccessExpression(expr) && expr.argumentExpression &&
+                isElementAccessExpression(expr) &&
                 (isStringLiteral(expr.argumentExpression) || isNumericLiteral(expr.argumentExpression)) &&
                 isNarrowableReference(expr.expression);
         }

src/compiler/checker.ts

@@ -21062,21 +21062,6 @@ namespace ts {
             const objectType = getAssignmentTargetKind(node) !== AssignmentKind.None || isMethodAccessForCall(node) ? getWidenedType(exprType) : exprType;
 
             const indexExpression = node.argumentExpression;
-            if (!indexExpression) {
-                const sourceFile = getSourceFileOfNode(node);
-                if (node.parent.kind === SyntaxKind.NewExpression && (<NewExpression>node.parent).expression === node) {
-                    const start = skipTrivia(sourceFile.text, node.expression.end);
-                    const end = node.end;
-                    grammarErrorAtPos(sourceFile, start, end - start, Diagnostics.new_T_cannot_be_used_to_create_an_array_Use_new_Array_T_instead);
-                }
-                else {
-                    const start = node.end - "]".length;
-                    const end = node.end;
-                    grammarErrorAtPos(sourceFile, start, end - start, Diagnostics.Expression_expected);
-                }
-                return errorType;
-            }
-
             const indexType = checkExpression(indexExpression);
 
             if (objectType === errorType || objectType === silentNeverType) {
@@ -29742,9 +29727,7 @@ namespace ts {
                                     name = ex.name.escapedText;
                                 }
                                 else {
-                                    const argument = ex.argumentExpression;
-                                    Debug.assert(isLiteralExpression(argument));
-                                    name = escapeLeadingUnderscores((argument as LiteralExpression).text);
+                                    name = escapeLeadingUnderscores(cast(ex.argumentExpression, isLiteralExpression).text);
                                 }
                                 return evaluateEnumMember(expr, type.symbol, name);
                             }

src/compiler/diagnosticMessages.json

@@ -459,10 +459,6 @@
         "category": "Error",
         "code": 1149
     },
-    "'new T[]' cannot be used to create an array. Use 'new Array<T>()' instead.": {
-        "category": "Error",
-        "code": 1150
-    },
     "'const' declarations must be initialized.": {
         "category": "Error",
         "code": 1155