LibJS: Invalidate cached environment coordinate after delete in global

Fixes the bug in interpreter when cached environment coordinate is not
invalidated after `delete` operator usage on global `this`.

Userland/Libraries/LibJS/Tests/operators/delete-global-variable.js

@@ -1,4 +1,5 @@
 a = 1;
+b = 42;
 
 test("basic functionality", () => {
     expect(delete a).toBeTrue();
@@ -7,3 +8,16 @@ test("basic functionality", () => {
         a;
     }).toThrowWithMessage(ReferenceError, "'a' is not defined");
 });
+
+test("delete global var after usage", () => {
+    let errors = 0;
+    for (let i = 0; i < 3; ++i) {
+        try {
+            b++;
+        } catch {
+            ++errors;
+        }
+        delete globalThis.b;
+    }
+    expect(errors).toBe(2);
+});