camera: remove 768x432 as a valid preview resolution

Video camera code will choose 768x432 as the preview resolution for
non-720p display devices when HD video recording resolution is selected
otherwise.

Change-Id: I5366831bf8576c8911da7f23883443178034365b
Camera: Fix CTS testPreviewPictureSizesCombination.

CRs-fixed: 346704

(cherry picked from commit 921dcbf654e2a1ac3ed585b15c917576814d87c0)
(cherry picked from commit 677870b791069b3b8e9aa347d6666e6f4c9581f5)

Change-Id: I6ec20790a8812dc2cae9933b29989a2f63450b16