[MXNET-618] Clojure package - move NDArray and Symbol Code generation to Automatic

[gigasquid]

Description

From feedback from the Clojure package PR #11205, this changes the automatic generation of the ndarray and symbol code from a manual step to an automatic compile-time (AOT) step. The generated code is no longer checked into git as well.

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [MXNET-$JIRA_ID], where $JIRA_ID refers to the relevant JIRA issue created (except PRs with tiny changes)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Code is well-documented:
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Changes

• Move ndarray and symbol code generation to compile time
• Remove generated code files from git
• Remove the alias to generate-code from the project file since it is now automatic

Testing

To test this change:

with lein test

1. Make sure there are no files in the src/org/apache/clojure_mxnet/gen directory
2. Run lein test
3. Tests should run fine and the generated files should be present in src/org/apache/clojure_mxnet/gen but ignored by git

with jars

1. Make sure there are no files in the src/org/apache/clojure_mxnet/gen directory
2. Run lein install to create target jar
3. cd examples/imclassification
4. run lein run to run the example with the installed jar

[marcoabreu]

Hey Carin, I can't review your PR on my phone due to the number of deleted files. Please excuse if this is already answered.

The two processes you described, are they already part of CI or how are we testing it? If something takes a long time, I'm happy to add it to nightly.

[gigasquid]

@marcoabreu - I put manual testings instructions there. The first part with lein test is what the CI does. The second part with jars is not covered by CI right now. It is creating the jars and then using them in another project. Eventually this is what I hope integration tests to cover.

For this PR, if CI tests are green, we are good to go.

If someone else wants to test out the with jars step manually, that would be great too.