Remove private header from encoder_example.
Remove private header from encoder_example.

Commit 9cd4263d8223 removed the actual dependency on the API, but
 left us still including the header that contained it.
This removes the unneeded #include as well.

luctrudeau/daala,KyleSiefring/daala,luctrudeau/daala,xiphmont/daala,ycho/daala,jmvalin/daala,KyleSiefring/daala,jmvalin/daala,xiph/daala,xiph/daala,KyleSiefring/daala,xiphmont/daala,ycho/daala,KyleSiefring/daala,HeadhunterXamd/daala,xiph/daala,kodabb/daala,HeadhunterXamd/daala,kodabb/daala,ycho/daala,xiphmont/daala,xiphmont/daala,ycho/daala,HeadhunterXamd/daala,jmvalin/daala,xiphmont/daala,kodabb/daala,ycho/daala,luctrudeau/daala,HeadhunterXamd/daala,luctrudeau/daala,luctrudeau/daala,kodabb/daala,xiph/daala,jmvalin/daala,KyleSiefring/daala,xiph/daala,jmvalin/daala,HeadhunterXamd/daala,kodabb/daala