[fuchsia] Disable timeline semaphore support.

The goldfish-opengl ICD doesn't support Vulkan timeline support
properly; we should disable it unconditionally on Fuchsia.

Test: vkreadback on FEMU w/ latest roll.
Fixed: 325639938
Change-Id: I534c3558c5bbe232f7e6c31520d7759d09ed7e5f
2 files changed