Gaia is removed from cosmos-sdk repository.
Few changes were required to make sure no packages depend on gaia subpackages.
CI config is amended accordingly.
Unnecessary targets are removed from Makefile.
Simulations run through a lightweight version of gaia renamed to simapp.
Closes: #4104
This fixes the "panic: Governance deposit amount must be a valid sdk.Coins amount, is 0stake" that can happen in the simulator if `DepositParams/MinDeposit` samples the integer `0`.