Document removal of cold_reads_to_omit in 2.2 and 3.0 NEWS.txt

Shouldn’t 2.2 be backwards compatible with 2.1?
The removal of the cold_reads_to_omit parameter in SizeTieredCompactionStrategy breaks backwards compatibility, wouldn't it be better to keep the same behaviour as in later 2.1 versions, the parameter is there but doesn’t do anything. The cold_reads_to_omit parameter should be removed in 3.0.
This could be fixed by applying the patch in CASSANDRA-9203 on the 2.2 branch.