[PATCH] Remove log2 define

[Wilco Dijkstra]

Corinna Vinschen wrote:

>> Since newlib now has a fast implementation of log2,
>
> Only if !__OBSOLETE_MATH

Is there any reason keep that old code, particularly for the rewritten double
precision functions? We now have a log2 that is both fast, accurate and
correct, which isn't true for the obsolete version.

Wilco