Always try pre-built external_libs from development branch
Always try pre-built external_libs from development branch

Summary:
Pre-built external_libs from the development branch are almost
always applicable to all builds in our workflow:

Recent review requests are forked from development, and
changes to master when preparing a release have the latest
changes from development merged in.

Doing it like this saves time during the release and for
building review-request diffs:

No need to wait for the external_libs_master branch
to build external_libs for master when there is no change compared to
development that was just merged in.

No need to have a multitude of prebuilt external_libs
for all feature/bugfix branches when there is no change from development
in order to speed up the code review build (which has not been done).

If there are still differences in external_libs, between the prebuilt
version and the required version for a particular buíld, then
they will be detected and external_libs will be rebuilt, no harm
done.

Ref T550. When this review request is accepted, then the Jenkins
jobs http://localhost:8080/job/openMHA/job/external_libs/ and
http://localhost:8080/job/openMHA/job/update_external_libs_branch/
should be adapted to only work with branch development.

Test Plan: Review and discuss.

Reviewers: pmaanen

Maniphest Tasks: T550

Differential Revision: https://dev.openmha.org/D104

HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA