Check return from DeleteKey correctly.

DeleteKey may legitimately return ErrorCode::UNIMPLEMENTED rather than
ErrorCode::OK, but the VTS test didn't allow that in all cases.  In many
case the return code was also left unchecked.

Test: adb shell/data/nativetest64/VtsHalKeymasterV3_0TargetTest/VtsHalKeymasterV3_0TargetTest
Bug: 62193967
Change-Id: I19a90a87850675b0700baf7409e57098e0584d54