Convert to use the FPGA PWM cycle synchronization

This removes the need for the pwm feedback wire.

Change-Id: I8af9252cc81fd00d3904e785356deffb2ee89b00
diff --git a/y2017/wpilib_interface.cc b/y2017/wpilib_interface.cc
index a5235c9..12e5760 100644
--- a/y2017/wpilib_interface.cc
+++ b/y2017/wpilib_interface.cc
@@ -465,7 +465,7 @@
     reader.set_autonomous_mode(0, make_unique<DigitalInput>(9));
     reader.set_autonomous_mode(1, make_unique<DigitalInput>(8));
 
-    reader.set_pwm_trigger(make_unique<DigitalInput>(7));
+    reader.set_pwm_trigger(true);
 
     ::std::thread reader_thread(::std::ref(reader));