Fix errors caught by aapt2

Remove dangling symlinks, which were ignored by aapt but cause
an error with aapt2.  Fixes:
packages/apps/Calendar/assets/backward: error: failed to open file.

Bug: 21548934
Bug: 79481102
Test: m java FORCE_AAPT2=true
Change-Id: I1fe884269ec59a348d611796c66a27887f6e720f
2 files changed