Remove unnecessary abstraction of classes.

Several utility classes were declared abstract, but there is no
intention of subclassing these classes. Instead opt for private
constructors where necessary to avoid instantiation and remove the
abstract keywords. Additionally make the classes final to clearly
indicate they are not intended to be subclassed.

Test: builds
Change-Id: I38bfe5f0685e4b333201c9c9fbb13b7aac8b4980