Fixed "Delete all unused declarations" to delete self-referential functions (#60888)

Author: Andarist

src/services/codefixes/fixUnusedIdentifier.ts

@@ -200,6 +200,9 @@ registerCodeFix({
                     else if (canDeleteEntireVariableStatement(sourceFile, token)) {
                         deleteEntireVariableStatement(changes, sourceFile, token.parent as VariableDeclarationList);
                     }
+                    else if (isIdentifier(token) && isFunctionDeclaration(token.parent)) {
+                        deleteFunctionLikeDeclaration(changes, sourceFile, token.parent as FunctionLikeDeclaration);
+                    }
                     else {
                         tryDeleteDeclaration(sourceFile, token, changes, checker, sourceFiles, program, cancellationToken, /*isFixAll*/ true);
                     }

tests/cases/fourslash/codeFixUnusedIdentifier_all_selfReferencingFunction.ts

@@ -0,0 +1,18 @@
+/// <reference path='fourslash.ts' />
+
+//// function fibonacci(n: number): number {
+////   if (n <= 1) {
+////     return n;
+////   }
+////   return fibonacci(n - 1) + fibonacci(n - 2);
+//// }
+//// 
+//// function other() {}
+////
+//// export {};
+
+verify.codeFixAll({
+    fixId: "unusedIdentifier_delete",
+    fixAllDescription: ts.Diagnostics.Delete_all_unused_declarations.message,
+    newFileContent: "\n\nexport {};",
+});