Revert "init: use read_file and write_file to implement do_copy builtin"

Bug: 36726045
Test: gts-tradefed run gts --abi x86 -m GtsMediaTestCases -t com.google.android.media.gts.MediaCodecCencTest#testCENC_DASH_FMP4_H264_360P_PLAYREADY_CENC
This reverts commit 82bac0de.

Change-Id: I3b754f429499daec804a0ad25529294216c39a40
(cherry picked from commit 281531bd)