Remove has_trivial_move trait from StringPool types

StringPool:entry* are not trivially moveable, as they contain Vector<>
objects.  The data in Vector<> is trivially moveable, but Vector<>
itself is a dynamic type with a vtable, which is not trivially
moveable.

Impact on aapt for frameworks-res is negligible, ~3%.

Bug: 31595853
Test: m -j framework-res
Change-Id: I562a46ef8934aed7aab5c5377db53d9cf64a08b9