[fpc-pascal] FSplit is deprecated

[Marco van de Voort]

In our previous episode, Bernd said:
> unixutil
> 
> another deprecated function that has not written any hint towards its
> replacement right behind the 'deprecated' keyword (where it would
> belong). The RTL documentation also does not contain any hints.

Unixutil is a barrel of leftovers of 1.0.x times, and mostly obsolete.

Originally they were used in the implementation of the unix unit internally
(then still called "linux") and mostly meant to implement the dos unit.

But in general since 2.0.x it is not recommended to use the dos unit anymore
unless it really is for old TP code (and even then I would consider
updating). This among others because of 255 char limitations of the
dos interface.

So use functions from 2.0.x like sysutils.extract*