Remove sdk_version: "core_platform_current"

This (effectively) reverts commit 3c979c33.

core_platform_current is the new default when no_framework_libs: true
so doesn't need to be specified anywhere.

Bug: 113148576
Test: build
Change-Id: I6bb6c1a0ea24437c8253dc5d8fabd37edabc9d3e