vcsui: Drop dead code for project tree VCS indicator color

vcs-added and vcs-changed (initially found in the CSS) were only mentioned in the vcsui tree addin, where the only state that changed, the two rgba colors in the struct, weren't ever used.

Effectively those were dead code, so this commit removes them. It's likely that the colored status indicator feature was dropped at one point, but that this part of the code was missed.

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I wonder if the code was made dead on purpose actually.