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.