Dex header cleanup and windows simplification

Remove a few unnecessary inclusions, move one missed header to
libdexfile.  Also use android-base utilities for file loading in
dexdump2 and dexlist.  (The utilities seem to work on Windows, where
mmap did not.)

Bug: 22322814
Test: make -j 50 test-art-host-gtest
Change-Id: I6e6de1895921f664a2280451b01e367649436200