dEQP-VK: Fix and inline the Image::getPixelOffset helper

dEQP-VK: Fix and inline the Image::getPixelOffset helper

The helper was wrong in a number of ways.  First, it tries to calculate
an offset to the particular mip level and array layer requested even
though the driver already provides that as part of the offset returned
by getImageSubresourceLayout.  If someone tried to use this with a
non-zero mip level or array layer they would get the wrong offset
because it would be added in twice.  Second, the calculation depended on
an array called mipLevelRectSizes array which was used but never
initialized.  This commit gets rid of the helper and just does the right
calculation inside MemoryOp::readLinear and MemoryOp::uploadLinear.

This affects the following groups of tests:

 - dEQP-VK.draw.*
 - dEQP-VK.dynamic_state.*
 - dEQP-VK.query_pool.*

Change-Id: If0da72023cbc437d2a13d60f83e1230f0f90ba39