Removed templated parameters from ReflectionClass#isInstance()

These templates were leading to false positives: assuming
an `object` is given as input, the inferred return
type would always have been `true`, which is obviously
not valid.

Removing them is the healthier alternative, for now.

Ref: https://github.com/vimeo/psalm/pull/8722#discussion_r1027102713

stubs/Reflection.phpstub

@@ -192,15 +192,7 @@ class ReflectionClass implements Reflector {
      */
     public function getModifiers(): bool {}
 
-    /**
-     * @template TCheckedObject of object
-     *
-     * @param TCheckedObject $object
-     *
-     * @return (TCheckedObject is T ? true : bool)
-     *
-     * @psalm-pure
-     */
+    /** @psalm-pure */
     public function isInstance(object $object): bool {}
 
     /**