Spring Remove support for setting default CacheAwareContextLoaderDelegate via system property

Since the ability to set a system property to change the default CacheAwareContextLoaderDelegate was only needed by the Spring Native project and should not be used by other projects, we should revert the changes made in conjunction with #27540.

Comment From: sbrannen

Team Decision: remove the feature since it is no longer needed and since keeping it would enable someone to accidentally disable AOT support in the TestContext framework (since DefaultCacheAwareContextLoaderDelegate now has built-in AOT support).