They are not duplicate,they are different files(may be different versions) in same package.
If you run apt-cache show libelf1 you will get,
Package: libelf1
Filename: pool/main/e/elfutils/libelf1_0.158-0ubuntu5.2_amd64.deb
Size: 37966
Filename: pool/main/e/elfutils/libelf1_0.158-0ubuntu5_amd64.deb
Size: 38320
Please refer launchpad.net/ubuntu/trusty/amd64/libelf1
