Bug 1844492 remove dom.input.showPicker pref r=emilio,saschanaz

Differential Revision: https://phabricator.services.mozilla.com/D184315

dom/webidl/HTMLInputElement.webidl

@@ -133,7 +133,7 @@ interface HTMLInputElement : HTMLElement {
   [Throws]
   undefined setSelectionRange(unsigned long start, unsigned long end, optional DOMString direction);
 
-  [Throws, Pref="dom.input.showPicker"]
+  [Throws]
   undefined showPicker();
 
   // also has obsolete members

modules/libpref/init/StaticPrefList.yaml

@@ -2992,12 +2992,6 @@
   value: @IS_NIGHTLY_BUILD@
   mirror: always
 
-# Is support for HTMLInputElement.showPicker enabled?
-- name: dom.input.showPicker
-  type: bool
-  value: true
-  mirror: always
-
 # Whether to allow or disallow web apps to cancel `beforeinput` events caused
 # by MozEditableElement#setUserInput() which is used by autocomplete, autofill
 # and password manager.