[machina] Remove RGBx888 VIM2 workaround

With [1], the VIM2 now correctly ignores the alpha channel for RGBx888
framebuffers, so we no longer have to modify bitmaps when blitting.

[1] https://fuchsia-review.googlesource.com/c/zircon/+/125122

Change-Id: I419c01ba1d6bc7fc4c4f2a249d59dd476efb49e1
1 file changed