refactor: remove non default colorschemes

[ChristianChiarulli]

No description provided.

[LostNeophyte]

can we use #3700 instead? has a deprecation warning

[kylo252]

I agree with @LostNeophyte, we should at least have a clear deprecation warning, and a fallback by checking if the plugin exists we already implement a fallback in #2982 😄 .

[cpea2506]

Do we have a plan to replace lvim.colorscheme with this option in the future? So users won't have to call the field twice if they want to customize some options in the colorscheme like below:

lvim.colorscheme = "lunar"
lvim.builtin.theme = {
	name = "lunar"
	lunar = {
		options = {
			-- option values
		}
	}
}

The new theme setting can be a string or a table:

lvim.builtin.theme = "lunar"
-- or
lvim.builtin.theme = {
	name = "lunar"
	options = {
		-- option values
	}
}

or shorter name with only lvim.colorscheme