Remove redundant chunk-coords passed into generate method

You can access the base chunk coordinates in the buffer.
This prevents people from confusing the generator for generating
a single chunk at once, instead of multiple chunks like it does.

Signed-off-by: Irmo van den Berge <bergerkiller@gmail.com>
Merge pull request #2243 from bergerkiller/master

Remove redundant chunk-coords passed into generate method