Restore enableWebfonts pref and remove uls-enable

This patch restores the enableWebfonts preference, stored inside
the uls-preferences blob. It existed as 'enable-webfonts' in
the past and was removed in
If735a733717596fae03042c5e277bd538bd8501f

Each wiki can be configured to load the fonts by default
using the new global variable $wgULSWebfontsEnabled.
Its default value is true (to load fonts).

This also removes the preference 'uls-enable', recently added in
I71b70d8ee7c3cad7f49b32e5dc494ef4fc1bdb2f

The initialization of ext.uls.webfonts.js is changed as well,
so that minimal webfonts JS library code is loaded,
and the rest is loaded only if a user requests it.

Bug: 60304
Change-Id: I49e812eae32266f165591c75fd67b86ca06b13f0

tests/browser/features/step_definitions/autonym_steps.rb

@@ -2,10 +2,6 @@ When(/^I am on the main page$/) do
 	visit MainPage
 end
 
-Then(/^I open Input panel of language settings$/) do
-	on(PanelPage).panel_input_element.when_visible.click
-end
-
 Then(/^I open Input side panel of language settings$/) do
 	on(PanelPage).panel_side_input_element.when_visible.click
 end