Make test_layer delete destroyed devices

Make test_layer delete destroyed devices

Destroyed devices need to be removed from the test_layer's created_devices
vector, so that it doesn't accidentally mistake dead devices for alive ones
when checking for whether a device extension is supported or not.

This caused multiple days of debugging headache as it caused sporadic test
failures due to the re-use of VkDevice handle values (which is caused by
the memory manager reusing allocations). Since a second VkDevice could share
the handle value of the first, and the first wasn't removed from the vector,
test_layer would use the data assocated with the first device by mistake.