removed 'static' keyword from 'private static enum'.

Hello
I did found 'private static enum'.
'static' keyword is unnecessary for enum type.
'Nested enum types are implicitly static(https://docs.oracle.com/javase/specs/jls/se8/html/jls-8.html#jls-8.9)'.
So I removed 'static' keyword from 'private static enum'.

https://github.com/apache/phoenix/pull/438

Thank you for reading.