Remove deprecated register in C++17
Fixes errors like
src/libnurbs/internals/varray.cc:76:5: error: ISO C++17 does not allow 'register' storage class specifier [-Wregister] register long ds = sgn(arc->tail()[0] - arc->prev->tail()[0]); ^~~~~~~~~
Signed-off-by: Khem Raj raj.khem@gmail.com