[GSS](7.2.z) UNDERTOW-1722 - Memory leak involving request attributes

With UNDERTOW-1573, attributes are no longer cleared from requests and we have a leakage when going from Session to Request to request attributes.
Please, see attached image for an example of a stack.
We need to clear attributes after the listeners are invoked so we don't break the fix for UNDERTOW-1573 while still preventing a memory leak.