Avoid passing encoding creation option to format drivers that don't support it

[sgillies]

See https://github.com/Toblerity/Fiona/issues/468#issuecomment-344111416: the GeoJSON driver warns that ENCODING isn't supported.

@mattayes the warning is harmless but we can avoid it.

[snorfalorpagus]

I can't see any way to ask GDAL which creation options are supported by a driver/dataset/layer. Do we need to build our own list for the drivers we support?

[sgillies]

According to http://www.gdal.org/gdal_8h.html#aec318ffe797555656fe678558c576b23 GDALValidateCreationOptions will validate options, and there's a hint about a GDAL_DMD_CREATIONOPTIONLIST driver metadata item.

Still, I think the immediate thing for me to do is to eliminate the encoding option in the GeoJSON case.

[snorfalorpagus]

Warning 6: driver MapInfo File does not support creation option ENCODING

Looks like MapInfo is the same.

[kurt-rhee]

KML driver as well

not recognized as a supported file format. driver KML does not support creation option ENCODING

[sgillies]

Done!