sync.profile: Point dependencies to an empty string

This means that we are going to use the same branch name for the
dependencies as the branch of the repository under test.

The only exception is qt3d which still uses the master branch.

Change-Id: If18ed7a691b9e8e32c1e9024fb241c5ee5374690
Reviewed-by: Alex <alexander.blasche@digia.com>
test: Mark tst_declarative_ui as insignificant

Task-number: QTBUG-31797
Change-Id: I50b3089c7a2563fc3c0c67f0dad9efe79cae3281
Reviewed-by: Alex <alexander.blasche@digia.com>
test: Mark tst_declarative_core as insignificant

Task-number: QTBUG-31798
Change-Id: I3ec1efe3044ec36938e72c4b07dad61784a699e7
Reviewed-by: Alex <alexander.blasche@digia.com>