remove references to arduino leonardo platform

the Userspace.mk was originall based on the Arduino.mk which
included some references to the leonardo arduino platform. these
are not needed for Userspace.mk
remove unused make targets

this patch removes some used make targets that are specific to
the arduino.
remove arduino parse_board_command

the Userspace.mk was based on the Arduino.mk. some commands like
the parse_board_command is not applicable to Userspace.mk
remove hex and eep targets

the hex and eep targets are not applicable to the Userspace.mk,
removing them and setting the default target as elf.