USBDevice: fix Disco L475VG target usb hal files

[0xc0170]

USB HAL header files were duplicated. These should be in STM root folder.

Tested

python tools/build.py -m DISCO_L475VG_IOT01A -t GCC_ARM -j 4 -c --silent --dsp --usb

Completed in: (85.86)s

Build successes:
  * GCC_ARM::DISCO_L475VG_IOT01A

cc @jeromecoutant @theotherjimmy

[theotherjimmy]

@0xc0170 I think that I got this in when I rebased @screamerbg's PR #4277. I would like to not rebase that PR yet another time, so I prefer to merge that PR over this one.

[0xc0170]

Ok, closing this one , lets make that big PR reviewed and integrated !