There seems to be 3 different macros to parse the boards.txt file.
This patch moves the PARSE_BOARD macro from Arduino.mk to Common.mk.
The PARSE_OPENCM and PARSE_TEENSY macros in Teensy.mk and OpenCM.mk
were removed and the common PARSE_BOARD is now being called from
everywhere.
Advantages of this fix are:
1. Less code, i.e. no redundant parse macros.
2. A single standardized algorithm to parse the boards.txt file.
