* Provide dedicated functions for deleteing accounts and storage trees
why:
Storage trees are always linked to an account, so there is no need
for an application to fiddle about (e.g. re-cycling, unlinking)
storage tree vertex IDs.
* Remove `delete()` and other cruft from API, `aristo_delete`, etc.
* clean up delete functions
details:
The delete implementations `deleteImpl()` and `delTreeImpl()` do not
need to be super generic anymore as all the edge cases are covered by
the specialised `deleteAccountPayload()`, `deleteGenericData()`, etc.
* Avoid unnecessary re-calculations of account keys
why:
The function `registerAccountForUpdate()` did extract the storage ID
(if any) and automatically marked the Merkle keys along the account
path for re-hashing.
This would also apply if there was later detected that the account
or the storage tree did not need to be updated.
So the `registerAccountForUpdate()` function was split into a part
which retrieved the storage ID, and another one which marked the
Merkle keys for re-calculation to be applied only when needed.
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