Remove ast_generic_v1.atd (#340)

It was experimental and it's not maintained nor used, so
let's get rid of it.

test plan:
see related PR in semgrep


- [x] I ran `make setup && make` to update the generated code after
editing a `.atd` file (TODO: have a CI check)
- [x] I made sure we're still backward compatible with old versions of
the CLI.
For example, the Semgrep backend need to still be able to *consume* data
	  generated by Semgrep 1.50.0.
See
https://atd.readthedocs.io/en/latest/atdgen-tutorial.html#smooth-protocol-upgrades
	  Note that the types related to the semgrep-core JSON output or the
	  semgrep-core RPC do not need to be backward compatible!

Co-authored-by: pad <[email protected]>
Co-authored-by: Martin Jambon <[email protected]>

Makefile

@@ -16,9 +16,6 @@ FILES= \
   semgrep_output_$(VER).ts \
   semgrep_output_$(VER).jsonschema \
   semgrep_output_$(VER).proto \
-  ast_generic_$(VER).py \
-  ast_generic_$(VER)_j.ml \
-  ast_generic_$(VER)_j.mli \
   Language.ml \
   Language.mli \
   lang.json \