LAG upgrade - 25: removing custom aggregator create API

Removed #custom #aggregator #create / #remove API in LAG module. The custom aggregator entries are #embedded in the #standard #aggregator entries and the standard aggregator create / remove API already handles the required functionality. Hence the redundant external API is being removed.

#LAG update 33 ...
[commit 0a76fda1aa99caf3fb55c5658b71bc4fb6f406ae] (https://github.com/nes-repo/NES-Open-Switch/commit/0a76fda1aa99caf3fb55c5658b71bc4fb6f406ae)