ThinkNode M6 repeater: disable leftover MESH_DEBUG/GPS_NMEA_DEBUG

The M6 is the only board whose simple_repeater env ships with MESH_DEBUG=1
and GPS_NMEA_DEBUG=1 enabled. MESH_DEBUG=1 adds a 5-second boot delay
(examples/simple_repeater/main.cpp) plus verbose per-packet serial prints on
the hot RX/TX path; GPS_NMEA_DEBUG=1 echoes every GPS UART character to the
serial console (MicroNMEALocationProvider.h). Every sibling repeater env
(M1, M3, t1000-e, RAK, Heltec) ships these off, and the M6 room_server env
in this same file already has them commented. Comment them out to match.

variants/thinknode_m6/platformio.ini

@@ -48,8 +48,8 @@ build_flags =
   -D ADMIN_PASSWORD='"password"'
   -D MAX_NEIGHBOURS=50
 ;  -D MESH_PACKET_LOGGING=1
-  -D MESH_DEBUG=1
-  -D GPS_NMEA_DEBUG=1
+;  -D MESH_DEBUG=1
+;  -D GPS_NMEA_DEBUG=1
 build_src_filter = ${ThinkNode_M6.build_src_filter}
   +<../examples/simple_repeater/*.cpp>
 lib_deps =