examples: clean up oudated code.

examples/basic/ctr.py

@@ -1,5 +1,5 @@
 from nmigen import *
-from nmigen.cli import main, pysim
+from nmigen.cli import main
 
 
 class Counter(Elaboratable):

examples/basic/gpio.py

@@ -1,4 +1,3 @@
-from types import SimpleNamespace
 from nmigen import *
 from nmigen.cli import main
 

examples/basic/sel.py

@@ -1,4 +1,3 @@
-from types import SimpleNamespace
 from nmigen import *
 from nmigen.cli import main
 

examples/basic/uart.py

@@ -103,7 +103,7 @@ if __name__ == "__main__":
 
     args = parser.parse_args()
     if args.action == "simulate":
-        from nmigen.back.pysim import Simulator, Passive
+        from nmigen.sim import Simulator, Passive
 
         sim = Simulator(uart)
         sim.add_clock(1e-6)