remove apcu_delete from the safe list

[Kharhamel]

apcu_delete returns false when the $key does not exist in the cache store, and error_get_last() returns null in this case.

[coveralls]

Pull Request Test Coverage Report for Build 280

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 45.242%

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Totals
Change from base Build 277:	0.0%
Covered Lines:	580
Relevant Lines:	1282

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💛 - Coveralls