Problem:
=========
As a part of MDEV-14398 patch, InnoDB added and removed
the tablespace from default encrypt list. But InnoDB removes
the tablespace from the default encrypt list too early due to
i) other encryption thread working on the tablespace
ii) When tablespace is being flushed at the end of
key rotation

InnoDB fails to decrypt/encrypt the tablespace since
the tablespace removed too early and it leads to
test case failure.

Solution:
=========
Avoid the removal of tablespace from default_encrypt_list
only when
1) Another active encryption thread working on tablespace
2) Eligible for tablespace key rotation
3) Tablespace is in flushing phase

Removed the workaround in encryption.innodb_encryption_filekeys test case.