Remove unused colors from palette.json

[ptbrowne]

At the moment, we generate a lot of utility classes from colors.
I think it'd be better to have fewer colors in what we make
available as utility classes since:

1. We should use semantic colors instead of absolute colors most of
   the time
2. It increases the build size

Here are some stats on the usage of utility classes for colors:

libs
  15 u-error
   8 u-weirdGreen
   5 u-coolGrey
   3 u-pomegranate
   2 u-slateGrey
   2 u-primaryColor
   1 u-valid
   1 u-bg-paleGrey
   1 u-bg-black
drive
   4 u-overlay
   3 u-pomegranate
   2 u-error
   1 u-coolGrey
banks
   3 u-valid
   3 u-slateGrey
   3 u-error
   2 u-coolGrey
   1 u-warn
   1 u-bg-chablis
notes
   1 u-charcoalGrey
contacts
   4 u-slateGrey
   4 u-bg-paleGrey
home
   3 u-pomegranate
   1 u-silver
settings
   1 u-lightishPurple
   1 u-dodgerBlue
   1 u-black

for app in libs drive banks notes contacts home settings
  echo $app
  pushd $app
  rg -o --no-filename "u-(bg-)?(black|white|paleGrey|silver|coolGrey|slateGrey|charcoalGrey|overlay|zircon|frenchPass|dodgerBlue|scienceBlue|puertoRico|grannyApple|emerald|malachite|seafoamGreen|brightSun|texasRose|chablis|yourPink|fuchsia|pomegranate|monza|portage|azure|melon|blazeOrange|mango|pumpkinOrange|lavender|darkPeriwinkle|purpley|lightishPurple|barney|weirdGreen|primaryColor|primaryColorLight|primaryContrastTextColor|valid|warn|error|errorBackgroundLight|primaryBackgroundLight|neutralBackground)" | sort | uniq -c | sort -rn
  popd
end

And we should not use the palette from cozy-ui directly:

libs
   3 palette['coolGrey']
   1 palette['white']
   1 palette['slateGrey']
drive
   2 palette['monza']
   2 palette['dodgerBlue']
   1 palette['emerald']
   1 palette['coolGrey']
banks
notes
contacts
   4 palette['coolGrey']
home
   2 palette['monza']
   2 palette['dodgerBlue']
   1 palette['emerald']
settings
   2 palette['emerald']

for app in libs drive banks notes contacts home settings
  echo $app
  pushd $app
  rg -o --no-filename "palette\[.(black|white|paleGrey|silver|coolGrey|slateGrey|charcoalGrey|overlay|zircon|frenchPass|dodgerBlue|scienceBlue|puertoRico|grannyApple|emerald|malachite|seafoamGreen|brightSun|texasRose|chablis|yourPink|fuchsia|pomegranate|monza|portage|azure|melon|blazeOrange|mango|pumpkinOrange|lavender|darkPeriwinkle|purpley|lightishPurple|barney|weirdGreen|primaryColor|primaryColorLight|primaryContrastTextColor|valid|warn|error|errorBackgroundLight|primaryBackgroundLight|neutralBackground).\]" | sort | uniq -c | sort -rn
  popd
end