Revert "Track libcore update of Map classes to jdk8u60"

May have broken stage-aosp-master since the CL from aosp-master was for
some reason only merged to mirror-aosp-master but no further.

Bug: 30911913

This reverts commit fb2ade3d.

Change-Id: I696d2b0636708fc6c73a53cd3cae36fa5bd0f173