Unused arguments in detect_targets.py

[theotherjimmy]

In particular, detect_targets.py accepts the following arguments that are not needed:

• -m/--mcu
• -t/--tool
• -c/--clean
• -o/--options
• -f/--filter we should probably make this one work instead of removing it.

These options print in the help. We should remove these options from the argument parser in detect_targets.py

[bridadan]

Should be a quick fix: https://github.com/mbedmicro/mbed/blob/master/tools/detect_targets.py#L43

Just need to replace that line with a fresh instance of argparse.

[ciarmcom]

ARM Internal Ref: IOTMORF-156