Turn the GHC assertion for rewards update from Conway and Shelley NEWEPOCH rules into STS assertions

[aniketd]

This issue is related to a pull request.

In the NEWEPOCH rule, we:

1. finalise the rewards calculation by forcing the pulser (calling completeRupd), and then
2. call updateRewards with the result. The assert in updateRewards needs to become an STS assertion.

That PR could not address this issue, due to the fact that an STS assertion does not have access to Globals which is required for completeRupd to run the pulsing calculation of rewards. In order to be able to solve this problem either the pulser finalisation function completeRupd should not have to depend on Globals, or we need to memoize the reward update result in the state to be able to pass it on to the PostCondition STS assertion.