apex_utils: do not use `deapexer list`

`deapexer list` doens't support erofs apex, but `deapexer extract` does.
Hence, we can use `deapexer extract` when signing the contents of an
apex.

Bug: 381185805
Test: releasetools_test
Change-Id: I226cbaaae0462598e6d9450428aa3b669284a521