USE_ECDSA is an undefined name in masternode.py

[cclauss]

Line 28 comments out USE_ECDSA but line 94 uses it.

flake8 testing of https://github.com/MatrixAINetwork/MatrixAIPoC_PY on Python 3.6.3

$ flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics

./core/src/election/masternode.py:94:16: F821 undefined name 'USE_ECDSA'
            if USE_ECDSA == 1:
               ^
1     F821 undefined name 'USE_ECDSA'
1