Refactor removing classes.dex for dexpreopt

Combining $(call dexpreopt-remove-classes.dex) into a
$(call copy-one-file) rule is hacky and error prone.  Make a helper
dexpreopt-copy-jar function that takes LOCAL_DEX_PREOPT and copies
the jar, removing the dex files if necessary.

Test: only description message changes to out/build-${TARGET_PRODUCT}.ninja
Change-Id: Id2fa2d18571ca01bc81302c912b8de25f3dde7a1