build: delete unused TAR variable in Makefile

The TAR variable is no longer used in the Makefile.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
build: delete unused INSTALL_PREFIX variable in Makefile

The INSTALL_PREFIX variable is no longer used in the Makefile.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
build: fix Makefile default goal

Include an empty Makefile default goal.
This prevent the 'install' target to run when make is called without arguments.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>