Bug 1321491 Part 1 - Remove unnecessary "layout.accessiblecaret.enabled" for Fennec. r=mtseng

Fennec has touch support, so enabling
"layout.accessiblecaret.enabled_on_touch" in all.js is sufficient.

MozReview-Commit-ID: 4Aa3g5eqt2F

--HG--
extra : rebase_source : c5fe085fe3d643dcf9f9a3732986954032566837

mobile/android/app/mobile.js

@@ -839,9 +839,6 @@ pref("reader.toolbar.vertical", false);
 // Whether to use the unified telemetry behavior, requires a restart.
 pref("toolkit.telemetry.unified", false);
 
-// Unified AccessibleCarets (touch-caret and selection-carets).
-pref("layout.accessiblecaret.enabled", true);
-
 // AccessibleCaret CSS for the Android L style assets.
 pref("layout.accessiblecaret.width", "22.0");
 pref("layout.accessiblecaret.height", "22.0");