Deprecate libjaylink Git submodule

Deprecate libjaylink Git submodule

libjaylink was integrated into OpenOCD as a Git submodule, because at
that time there was no official release and no packages for it.
Today there are libjaylink packages for most popular distributions [1].

Removing libjaylink from OpenOCD reduces build complexity in both
projects and makes them more flexible with respect to the build system,
for example.

Disable the libjaylink submodule by default and announce it as
deprecated feature that will be removed in the future. This gives
package maintainers time to package libjaylink if not already done.

[1] https://repology.org/project/libjaylink/versions

Change-Id: I6166ba4757aee5c89a0506de867072f58fa5ec4b
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/7129
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>