Revert the CErc20Delegator back to slightly less optimized version

[jflatow]

Addresses #39 by reverting the contract to the previous form used by cDAI.

[codecov-commenter]

Codecov Report

Merging #48 into master will decrease coverage by 1.74%.
The diff coverage is 48.43%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
- Coverage   50.38%   48.63%   -1.75%     
==========================================
  Files          47       42       -5     
  Lines        4077     3979      -98     
  Branches      515      506       -9     
==========================================
- Hits         2054     1935     -119     
- Misses       2023     2044      +21     

Impacted Files	Coverage Δ
contracts/CErc20Delegator.sol	68.99% <48.43%> (+26.24%)	⬆️
contracts/CToken.sol	70.97% <0.00%> (-11.02%)	⬇️
tests/Contracts/ComptrollerHarness.sol	47.29% <0.00%> (-10.35%)	⬇️
contracts/CErc20.sol	72.88% <0.00%> (-3.39%)	⬇️
tests/Contracts/CErc20Harness.sol	28.29% <0.00%> (-0.98%)	⬇️
tests/Contracts/Structs.sol
tests/Contracts/Const.sol
tests/Contracts/MockMCD.sol
contracts/DAIInterestRateModelV3.sol
contracts/JumpRateModelV2.sol
... and 1 more

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[jflatow]

These coverage drops should be addressed for a new cToken

[hayesgm]

I think coverage looks pretty good here

[jflatow]

This PR exists for the sake of deployers of future cTokens (linked elsewhere, does not need to remain open).