Temporarily remove PersistentCacheOptions from persistent_cache_tier.h to fix unity...

Temporarily remove PersistentCacheOptions from persistent_cache_tier.h to fix unity build

Summary:
PersistentCacheOptions class in persistent_cache_tier.h is not used any where yet in the code base
but it break the unity build because it have the same name as PersistentCacheOptions in table/persistent_cache_helper.h

Remove it temporarily, and the @krad can add it again with a different name when we start using it

Test Plan:
make unity_test -j64
make check -j64

Reviewers: kradhakrishnan, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D59349