tests/extmod: Skip soft machine.Timer test on esp32 port.

Also rename the test to reflect that it's a soft timer test.
Signed-off-by: Angus Gratton <angus@redyak.com.au>

tests/extmod/machine_timer.py → tests/extmod/machine_soft_timer.py

-# test machine.Timer
+# test "soft" machine.Timer (no hardware ID)
+import sys
+
+
+if sys.platform == "esp32":
+    print("SKIP")  # TODO: Implement soft timers for esp32 port
+    raise SystemExit
+
 
 try:
     import time, machine as machine