Remove ExtraBiomeHeight :(

Sorry cuitpoisson. There is currenlty some duplicated code, but more
importantly it breaks TerrainMode:OldGenerator.
The original pull request did have some more issues, like filling an
array with 0 or having code that didn't do anything but wasting CPU
time.

You're of course free to submit a new pull request that doesn't have
those two issues. What would also be nice if it didn't create an array
at all. Maybe there are other ways to implement it? A more descriptive
setting name than ExtraBiomeHeight would also be nice.

(cherry picked from commit 16d436b89b8d95a55f0d341da1f6d58d745b1bd2)