Fix cleanup of debug.vulkan.layers property

The CtsGpuToolsHostTestCases tests cause other vulkan tests failed in
vkCreateInstance() with error VK_ERROR_LAYER_NOT_PRESENT.

The cleanup() tries to clear the property of debug.vulkan.layers to
"\'\"\"\'". However, the executeAdbCommand() sets the "" string to the
property as [debug.vulkan.layers]: ['""']. This adds a layer of
name "" to the implicit layer list but not in the libvulkan global
list g_instance_layers. Eventually, following Vulkan tests in other
modules fail with VK_ERROR_LAYER_NOT_PRESENT  if calling
VK_CALL(vkCreateInstance(...)).

After this change, the property is set as [debug.vulkan.layers]: []

Bug: 144814602
Test: cts-tradefed run cts -m CtsGpuToolsHostTestCases
      cts-tradefed run cts -m CtsGraphicsTestCases
        -t android.graphics.cts.VulkanPreTransformTest#
        testVulkanPreTransformNotSetToMatchCurrentTransform
      cts-tradefed run cts -m CtsSkQPTestCases
        -t org.skia.skqp.SkQPRunner#unitTest_VulkanHardwareBuffer_CPU_Vulkan

Change-Id: I65f314f144c1ba4dcf8d6dd749c4b76fb4b90c1c
Merged-In: I65f314f144c1ba4dcf8d6dd749c4b76fb4b90c1c