Removed deprecated 'register' storage class specifier.

clang-3.5.0 now complains about them: warning: 'register' storage class specifier is deprecated [-Wdeprecated-register]

Modern compilers should know better what registers to assign. In addition, modern CPUs (amg64) have many more registers and heuristics possibly observed when those 'register' specifiers were set are now most likely obsolete.