Remove OS_* functions not used in netXTransport toolkit

The following functions are defined in OS_Dependent.h:

• OS_Memmove()
• OS_Strcspn()

Additionally, a stub of OS_Strcspn() is also supplied in OS_xxx.c template file.

These functions are not used by netXTransport toolkit and thus shouldn't be defined as 'dependent'.
This also affects the netXTransport toolkit documentation, although it is incomplete:
OS_Memmove() is not part of the OS_* function overview table and OS_Strcspn() has no detailed description.

As far as it can be traced, OS_Strcspn() is only used for Windows implementation for netXAPI - this is not part of the netXTransport toolkit (yet).

While each implementation is free to further abstract OS related functionality (and facilitate the OS_* API scheme), these should only be added locally.