Math: Remove aqua and fuchsia from the Elements Dock

We can remove these colors from the UI because these colors are equal to
cyan and magenta, and will be useful just in the import/exports filters. If the
user still wants to use aqua and fuchsia, they can type them in the Math editor.

Change-Id: Ia93d458e07b218aa007ec43bd490f774e5b4ea5b
Reviewed-on: https://gerrit.libreoffice.org/12467
Reviewed-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
Tested-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>