Remove unnecessary BUILD_NAMEDTENSOR from interned_strings.h (#25938)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25938
It doesn't matter whether or not we expose these for namedtensor /
non-namedtensor builds.
Test Plan: - [namedtensor ci]
Differential Revision: D17291249
Pulled By: zou3519
fbshipit-source-id: a5aac77469e28198f63967396e2bdb1ec15bad97