swapchain: Fix MAILBOX and SHARED presentation modes

This change undoes two previous changes and fixes the original
performance problem reported with b/182887411.  By default, Vulkan
swapchains should use:

- 3 images for FIFO (unless limited or increased from below)
- 1 images for SHARED

This reverts the following commits:

- commit 148bad07.
  "swapchain: increase the minimal buffer count to 3"
- commit ef14146f.
  "swapchain: always return a signle image for shared presentation mode"

Test: Manual testing with additional logging
Bug: 204105805
Bug: 182887411
Bug: 197790618
Change-Id: I9902d11aadf946a51c3f74e1462faf620a84a977