releng: Targets updates for Mars.2 and 4.6M6

releng: Targets updates for Mars.2 and 4.6M6

- Update 4.5 target with final Mars.2 update sites, use
non-composite where possible as they should not change (speeds up
dependency resolution)
- Update staging (4.6) target to not use the simrel update site, as
per recommendation by simrel team. Update update sites to latest
miletones; this required to fix the product dependencies. Luckily
those work with the 4.5 target too.

Change-Id: I39db87c315e7ee94a33c8b6c99b45ab86c81b1ad
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/68843
Reviewed-by: Hudson CI
Reviewed-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Tested-by: Alexandre Montplaisir <alexmonthy@efficios.com>