Remove EXT_SYNC_TST_N
Remove completely EXT_SYNC_TST_N signal along with associated T1, R1;
initially it was thought of as a way to make the PTS testing of the
board without needing any external pulse generator.
However, as the LEMO is a vital part of the design, checking its
connectivity is important and cannot be replaced by the
EXT_SYNC_TST_N.
Moreover the EXT_SYNC_TST_N could even damage the circuitry if the
transistor is enabled at the same time as pulses are arriving through
the LEMO.
Note also that in the PTS the LEMO is finally tested using the reference
voltage source in the USB relay box, so there is no need for a pulse
generator.