art: JVMTI unhiding API cleanup

This is a follow-up commit to 751510 to use the dex_file UnhideApis()
function instead of reimplementing the unhide iterators.

Test: art/test/testrunner/testrunner.py --interp-ac --target \
      -t 980-redefine-object -t 983-source-transform-verify

Change-Id: Ib3e872aa9a350cdf2b1461373735a99d956b5a38
Signed-off-by: Anestis Bechtsoudis <anestis@census-labs.com>