SkiaVkRenderEngine: Do not cache textures with protected contexts

`SkiaRenderEngine::mTextureCache` is not used with protected contexts
with the SkiaVk back-end.  This avoids crashed caused by using a
VkImage with a VkDevice that it wasn't created with.

Test: Face unlock training
Bug: 271907068
Bug: 264475961
Bug: 267295152
Change-Id: I1296539677ae63be63614ab2464dbb55b32276cd