[DISCUSS] Drop support for java 1.7 on the 1.2, 1.3 and 1.4 branches

[Thomas D'Silva]

We have traditionally followed HBase's java support (see
https://hbase.apache.org/book.html#basic.prerequisites). The
phoenix-queryserver module has a dependency on Avatica which does not
support Java 1.7. The phoenix-spark module depends on spark 2.3.2 which
also does not support Java 1.7. Do folks feel we should continue to provide
support Java 1.7 on the 1.x branches?