Talked this over with Nan -- Nimbus allows JSON'ed data as variable types, and we should use that to store weather suggestion keywords instead of the quick suggest config in remote settings. It doesn't make a lot of sense to use the RS config because we wouldn't want to change the keywords while experiments are active, and there are no plans right now to enable weather suggestions by default for the whole Suggest population. Using a Nimbus var ties the keywords to specific experiments while still allowing us to modify them right up until the moment any experiment ships.

One drawback is it makes it a little harder for people to manually test the keywords in the absence of an experiment, but that's solvable (by setting up an experiment on stage, running a JS snippet to install a mock experiment, or force enrolling in an actual experiment). We could give the variable a fallback pref and then people could set the pref, but that's extra complication since there's no other reason to use a fallback pref for this.

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.

https://hg.mozilla.org/mozilla-central/rev/75dd0ccb7d55