Do not increase mockTime when mining EVM block.

Anvil now (foundry-rs/foundry#9160) supports
blocks with constant timestamp, so there is no need to explicitly
bump the mock time when generating a new block (it can remain the same).

This simplifies testing logic potentially, as tests do not need to
expect increasing timestamps after setting a mock time.

xayax/eth.py

@@ -281,9 +281,6 @@ def mine (self):
       self.rpc.evm_mine ()
     else:
       self.rpc.evm_mine (self.mockTime)
-      # We need to bump the mock time at least by one second
-      # so the next block can be mined, too.
-      self.mockTime += 1
 
   def deployContract (self, addr, data, *args, **kwargs):
     """