boards: Remove executable bit on various non-executable files

boards/msba2-common/tools/flash.cmd

boards/nucleo-f103/Makefile

boards/nucleo-f103/Makefile.features

boards/nucleo-f103/Makefile.include

boards/nucleo-f103/dist/openocd.cfg

boards/nucleo-f103/include/board.h

boards/nucleo-f302/Makefile

boards/nucleo-f302/Makefile.features

boards/nucleo-f302/Makefile.include

boards/nucleo-f302/board.c

boards/nucleo-f302/dist/openocd.cfg

boards/nucleo-f302/include/board.h

boards/nucleo-f302/include/periph_conf.h

boards/nucleo-f303/Makefile

boards/nucleo-f303/Makefile.features

boards/nucleo-f303/Makefile.include

boards/nucleo-f303/board.c

boards/nucleo-f303/dist/openocd.cfg

boards/nucleo-f303/include/board.h

boards/nucleo-f303/include/periph_conf.h