moved platform_constants.h from openair2 to common directory
removed unused or dead code like MAC_XFACE or NB_THREAD_INST or unused functions
removed several files xxx_vars.h to make regular C code style: declare extern globals in a .h file, include this .h in all files that reference these globals and ALSO in the .c file that implement these globals
this work is still partial, but there was already a lot of modified files, so i will make more MRs
transformed variable constants into static const when it is constant
