remove the alias definition for symbolic color names

When using symbolic color names, we can drop the redefinition of the fill and draw colors.

This greatly reduces the file size. A fallback mechanism ensures the definitions are done as usual if either

 1. the maximal number of colors are exhausted or
 1. symbolic color names are switched off.
Well, kind of. I used 128 characters for the buffer and `colorstr` has a maximum of 10. I would have to call ´strlen` in any case to get the correct length and strcpy does that already. To make it super-safe, I could use `strncpy` with `n=MIN(strlen(colorstr), 128)` and set `dest[127] = '\0'`. What do you think?