Remove unused Graphic3d_Strips

Clang gives the following new warnings with 6.7.1:

src/Graphic3d/Graphic3d_Strips.cxx:248:7: warning:
template argument uses local type 'edg' [-Wlocal-type-template-args]
Standard::Free(cedge);

src/Graphic3d/Graphic3d_Strips.cxx:251:3: warning:
template argument uses local type 'edg' [-Wlocal-type-template-args]
Standard::Free(edges);

src/Graphic3d/Graphic3d_Strips.cxx:889:7: warning:
template argument uses local type 'edg' [-Wlocal-type-template-args]
Standard::Free(cedge);

src/Graphic3d/Graphic3d_Strips.cxx:892:3: warning:
template argument uses local type 'edg' [-Wlocal-type-template-args]
Standard::Free(edges);

This is allowed per C++11, however, this is prohibited in C++03. Better to make the template a global type.