This reverts commit fecfaacbaf.
Although this typedef is still useless, it's useful to check the sanity of
the names of template parameters of the periodic traits classes. If some
template paremeters are named like typedefs of the kernel (which is valid code,
but not ideal) some compilers will bug and fail to compile.
See also commit cbde108708
Mael Rouxel-Labbé
1378280c79