The `--jobs` parameter that some scripts defined was not used anywhere
in jenkins or mantle. So the value of the parameter always ended up
being equal to `${NUM_JOBS}` set by `common.sh`. Also, even if the
`--jobs` parameter was used for some script, that script usually
didn't forward the jobs value to other scripts, so the other scripts
ended up using `${NUM_JOBS}` again. Also, the `${FLAGS_jobs}` variable
was used by some functions in the build library, and those functions
were sometimes invoked by scripts that didn't define the
`${FLAGS_jobs}` variable. It is tedious to track which script should
actually define the parameter, and where it should be forwarded.
Just get rid of this half-working pretense. If you want to affect how
many jobs `emerge` uses, export the `NUM_JOBS` environment variable
before calling any script.
For `EMERGE_FLAGS` and `REBUILD_FLAGS` we unconditionally specify the
`--jobs` flag's value to `${NUM_JOBS}` because they are passed to
`emerge`. On the other hand we drop the `--jobs` parameter from the
`UPDATE_ARGS` variable, because this variable passed to `setup_board`
or `update_chroot`, which don't have this flag any more.
They end up using emerge_to_image which needs uses the `$FLAGS_jobs`
parameter. Seems like new portage does not like getting the parameter
like `--jobs=` (with an empty value).
