VPN-6213 part 4: Remove unused colors

[mcleinman]

Description

Pulling out all unused colors. At one point I changed all addTransparency(someColorName, 0.0) to color.transparent but that led to bugs. I left a comment to try to steer others away from this same trap.

From my testing, there are no missing colors when using the app. The logs do have some statements like QML MZInputBackground: The current style does not support customization of this control (property: "background" item: MZInputBackground_QMLTYPE_133(0x6000020bebc0, parent=0x0, geometry=0,0 0x0)). Please customize a non-native style (such as Basic, Fusion, Material, etc). For more information, see: https://doc.qt.io/qt-6/qtquickcontrols2-customize.html#customization-reference (MZSearchBar.qml:41), but this is unrelated to VPN-6213 - it exists on main as well.

This builds on #10015, which in turn builds on #10014, which in turn builds on #9983. All 3 have been merged into main.

There will be one more color-related PR coming, built on top of this. It will better structure all of this for swapping in new themes.

Reference

VPN-6213

Checklist

• My code follows the style guidelines for this project
• I have not added any packages that contain high risk or unknown licenses (GPL, LGPL, MPL, etc. consult with DevOps if in question)
• I have performed a self review of my own code
• I have commented my code PARTICULARLY in hard to understand areas
• I have added thorough tests where needed