fix(api): revert ES2021 target

.changes/revert-es2021.md

@@ -0,0 +1,5 @@
+---
+"api": patch
+---
+
+Revert target back to ES5.

tooling/api/tsconfig.json

@@ -2,7 +2,6 @@
   "compilerOptions": {
     "strict": true,
     "allowJs": true,
-    "target": "es2021",
     "esModuleInterop": true,
     "baseUrl": ".",
     "paths": {