Remove build_travis.py NUCLEO_F412ZG usb tests which requires other commits.

Author: simonqhughes

tools/build_travis.py

@@ -190,7 +190,6 @@
      "toolchains": "GCC_ARM",
      "tests": {""     : ["MBED_2", "MBED_10", "MBED_11", "MBED_16"],
                "rtos" : ["RTOS_1", "RTOS_2", "RTOS_3"],
-               "usb"  : ["USB_1", "USB_2" ,"USB_3", "USB_10", "USB_11"],
              }
     },
     {"target": "NUCLEO_F429ZI",