Set the char limit for "low light mode" to NONE.

There is plenty of space for this string and it doesn't really need a
character limit. The localization team has already said that the
current limit is too small.

Bug: 416255741
Test: manually
Flag: EXEMPT resource change
Change-Id: Ie25a7077bdee6c05bb0ac7e80fd6b2e20f0beda5