Pack libsquashfs_utils.so into otatools.zip.

Overlooked the transitive dependency on this lib in my previous CL that
packs libfec.so.

Bug: 122280472
Test: Build `otatools.zip`. Unzip and check that
      `ldd bin/delta_generator` no longer shows any missing lib.
Change-Id: I7b633ea870f05b86ee7760c736dac7c74dee5dc2