Don't erase key from s_new_ce_keys on eviction

Erasing a key from s_new_ce_keys is equivalent to destroying it, so it
shouldn't be done when the key is merely being evicted.

This didn't matter in practice since eviction requests don't come in
before the key gets persisted, but fix this to avoid confusion.

Test: see I7f11a135d8550618cd96013f834cebd54be5ef84
Change-Id: I28412f243925b5a7242449b617fe9de9c90912b6
Merged-In: I28412f243925b5a7242449b617fe9de9c90912b6
(cherry picked from commit 3529302e)