This reverts the changes from D168757 bug 1814795 related to remote settings. It
moves the weather keywords from the config in remote settings to a new Nimbus
variable called `weatherKeywords`. Bug 1817038 has more context.
It also adds another variable called `weatherKeywordsMinimumLength` that lets
the user type prefixes of the keywords instead of the full strings. This is
similar to how sponsored and Wikipedia suggestion keywords contain prefixes,
except here Firefox is computing the prefixes from the full keywords instead of
assuming that the prefixes are in the keyword data.
It also removes the `weather.zeroPrefix` pref added in D168757. Instead, the
weather suggestion is triggered on zero prefix if a Nimbus experiment isn't
active or if the experiment doesn't define `weatherKeywords`.
Finally, it makes one unrelated change: The user's search string can now contain
trailing spaces and still match a weather keyword. I don't think it makes sense
for the weather suggestion to be shown when you type "weather" but then it goes
away after you type a space.
Differential Revision: https://phabricator.services.mozilla.com/D169977
ee3004c674