Remove support for ropsten and kovan

[tuturu-tech]

The networks are deprecated as of last year.

crytic-compile/crytic_compile/platform/etherscan.py

Lines 38 to 39 in 10104f3

	"ropsten:": ("-ropsten.etherscan.io", "ropsten.etherscan.io"),
	"kovan:": ("-kovan.etherscan.io", "kovan.etherscan.io"),