Remove libdl from shared_libs

This entry is redundant, as system_shared_libs by default includes
libdl.

This should be a no-op change for the current build system, but avoids
an issue on the alternative (experimantal) build system, Bazel.

Test: md5sum libutils.so before/after on aosp_flame, verified no changes
Change-Id: I18f6e67c3e23299a0f1e0ef530a0a809b068dc03