Delete ParcelableString, add StringParceledListSlice

Both inherit from package private BaseParceledListSlice.

This is still bad, but it's not as bad. The existing code that uses
this can just do Foo.bar().getList() now instead of having to marshal
to and from an oddball type at either end as well.

In the longer term ParceledListSlice<> should be eliminated, but it's
not clear how far into the future that is going to happen.

Test: runtest -x services/tests/servicestests/src/com/android/server/devicepolicy/DevicePolicyManagerTest.java
Test: runtest -x core/tests/coretests/src/android/content/pm/ParceledListSliceTest.java
Change-Id: Ie69b96b5215d6e04990f6d31345772cdfee21d78