Fix removal of inaccessible devices

[nasahlpa]

When having multiple ChipWhisperer scopes attached and the user permissions for accessing one these scopes is missing, cw.scope() failes:

>>> import chipwhisperer as cw
>>> scope = cw.scope()
[<usb1.USBDevice object at 0x7f7dcc43cd90>]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/venv/src/chipwhisperer/software/chipwhisperer/__init__.py", line 384, in scope
    scope_type = get_cw_type(**kwargs)
  File "/opt/venv/src/chipwhisperer/software/chipwhisperer/common/utils/util.py", line 522, in get_cw_type
    device = cwusb.find(serial_number=sn, idProduct=possible_ids, hw_location=hw_location)
  File "/opt/venv/src/chipwhisperer/software/chipwhisperer/hardware/naeusb/naeusb.py", line 353, in find
    sns = ["{}:{}".format(dev.getProduct(), dev.getSerialNumber()) for dev in dev_list]
  File "/opt/venv/src/chipwhisperer/software/chipwhisperer/hardware/naeusb/naeusb.py", line 353, in <listcomp>
    sns = ["{}:{}".format(dev.getProduct(), dev.getSerialNumber()) for dev in dev_list]
  File "/opt/venv/lib/python3.8/site-packages/usb1/__init__.py", line 2003, in getProduct
    return self.open().getProduct()
  File "/opt/venv/lib/python3.8/site-packages/usb1/__init__.py", line 2055, in open
    mayRaiseUSBError(libusb1.libusb_open(self.device_p, byref(handle)))
  File "/opt/venv/lib/python3.8/site-packages/usb1/__init__.py", line 127, in mayRaiseUSBError
    __raiseUSBError(value)
  File "/opt/venv/lib/python3.8/site-packages/usb1/__init__.py", line 119, in raiseUSBError
    raise __STATUS_TO_EXCEPTION_DICT.get(value, __USBError)(value)
usb1.USBErrorNoDevice: LIBUSB_ERROR_NO_DEVICE [-4]

Although the get_possible_devices function in naeusb checks whether permissions are fine, the removal in the dev_list is incorrectly implemented. Instead of iterating over the list and removing items, the iteration should happen over a copy of the list.