doc: wrong description about compaction picking in Leveled Compaction wiki page

[Leveled Compaction](https://github.com/facebook/rocksdb/wiki/Leveled-Compaction) says:

>(if the file size is smaller than level0_file_num_compaction_trigger, compaction won't trigger from level 0, no matter how big the score is)

Since `level0_file_num_compaction_trigger` is a small value as a file size (its default value is `4`) , I think that such a comparison does not make much sense. And I browsed the source code and but failed to find the code which does the comparison. So I think that the above sentence should be removed.