Drop subgroup size requirement for uniform control

Drop subgroup size requirement for uniform control

The uniform control tests were using a required subgroup size without
checking for support. In fact, the only requirement is that the two
shaders in each test run with the same subgroup size. This is guaranteed
for all pipelines unless the varying size feature is enabled, so the
required subgroup size is not needed.

Components: Vulkan
VK-GL-CTS issue: 2576
Affects: dEQP-VK.subgroups.subgroup_uniform_control_flow.*control.*

Change-Id: Id1bf77a040ca6183b1ce237ae5f3bcda909c716c
(cherry picked from commit dbd42247ae8f885470fde4dbb3efccdb8c2e1134)