Remove unnecessary methods/fields of DefaultsModule/Base

The commonProperties and defaultsVisibilityProperties fields are only
used as containers for default values for properties and only within
the InitDefaultsModule() and so can be removed and replaced with an
empty structure instead.

Test: m checkbuild and TH
Change-Id: Ic5038d6b84b33afdf4859ced08e59871b9cde4a2