## Description
In Osmosis' simulation, we were observing that a large percent of the time was spent within SimulateParamChangeProposalContent, in particular within the composed key function. This is from a trace of our simulator running for 10 minutes:
<img width="931" alt="Screenshot 2021-06-08 at 2 32 28 PM" src="https://user-images.githubusercontent.com/6440154/121238788-16cdd000-c85e-11eb-8251-94537e69f8ce.png">
~This change lowers the number of calls to ComposedKey() by a factor of 3, and speeds up the underlying ComposedKey function. (sprintf is not particularly efficient for string concatenation, https://dev.to/pmalhaire/concatenate-strings-in-golang-a-quick-benchmark-4ahh ). After these change, the effect of ComposedKey() can no longer be seen in the profiler outputs.~
~This change does not change the result of the simulator on a given seed.~
See https://github.com/cosmos/cosmos-sdk/pull/9481#issuecomment-857119210 for description of changes.
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