patch 8.2.4602: Vim9: not enough test coverage for executing :def function

Problem:    Vim9: not enough test coverage for executing :def function.
Solution:   Add a few more tests.  Fix uncovered problem.  Remove dead code.
diff --git a/src/proto/vim9instr.pro b/src/proto/vim9instr.pro
index be41d7c..8da5597 100644
--- a/src/proto/vim9instr.pro
+++ b/src/proto/vim9instr.pro
@@ -19,8 +19,8 @@
 int generate_PUSHSPEC(cctx_T *cctx, varnumber_T number);
 int generate_PUSHF(cctx_T *cctx, float_T fnumber);
 int generate_PUSHS(cctx_T *cctx, char_u **str);
-int generate_PUSHCHANNEL(cctx_T *cctx, channel_T *channel);
-int generate_PUSHJOB(cctx_T *cctx, job_T *job);
+int generate_PUSHCHANNEL(cctx_T *cctx);
+int generate_PUSHJOB(cctx_T *cctx);
 int generate_PUSHBLOB(cctx_T *cctx, blob_T *blob);
 int generate_PUSHFUNC(cctx_T *cctx, char_u *name, type_T *type);
 int generate_AUTOLOAD(cctx_T *cctx, char_u *name, type_T *type);