Remove 4K min size from dedicated image tests

Remove 4K min size from dedicated image tests

The tests dEQP-VK.memory.mapping.dedicated_alloc.image.*
all create an image with a minimum size of 4Kx4K, so the
tests in this subgroup  test the exact same image size
regardless of what size the test itself is supposed to be
testing.

This change removes the 4Kx4K minimum to enable
the test to actually test multiple sizes of images.

Affect:

dEQP-VK.memory.mapping.dedicated_alloc.image.*

Components: Vulkan

VK-GL-CTS issue: 1118

Change-Id: I2ba9fa671f20eeb9bfa8b14972c903ac20875425