Remove Modules() from BootclasspathFragmentApexContentInfo.

The Modules() method was for the ART boot image in the ART APEX. It's no
longer needed because we don't install the ART boot image in the ART
APEX anymore.

Bug: 290583827
Test: m nothing
Change-Id: I674a5fa1ed18908413a64129df5947c7d26e638e