Summary
-------

Drop support for "`7`" from `javac`'s `-source`, `-target`, and `--release` options.

Problem
-------

JDK 7 shipped over a decade ago; continued support for that 7 increases maintenance costs of `javac` and is outside of the spirit of the policy published in JEP 182.

Solution
--------

Drop the 7 from the set of supported values..

Specification
-------------

The value "7" is not listed in the relevant `javac -help` output: 

      --release <release>
            Compile for the specified Java SE release. Supported releases: 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20
    ...
      --source <release>, -source <release>
            Provide source compatibility with the specified Java SE release. Supported releases: 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20
    ...
      --target <release>, -target <release>
            Generate class files suitable for the specified Java SE release. Supported releases: 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20