ReaderUI: Properly neuter gesture handling from InputContainer modules

None[1] of them actually rely on their own onGesture handler, they
all register their own stuff to ReaderUI's.
Hotfix #9710 revealed that the way this was handled didn't exactly
work as expected ;).

The only thing that consumes ges_events is InputContainer's onGesture
method. All these modules *extend* InputContainer, but none of them
*implement* a custom onGesture, so self.onGesture = nil was just a NOP,
they always access InputContainer's method via inheritance.
If we actively want to neuter it, we *have* to implement it in that
module (with a NOP).

[1] The exception being ReaderZooming, but that only when in flip mode.

frontend/apps/reader/modules/readerlink.lua

@@ -106,8 +106,13 @@ function ReaderLink:init()
         G_reader_settings:saveSetting("swipe_link_footnote_popup", nil)
         G_reader_settings:saveSetting("footnote_link_in_popup", true)
     end
+
+    -- delegate gesture listener to readerui, NOP our own
+    self.ges_events = nil
 end
 
+function ReaderLink:onGesture() end
+
 function ReaderLink:onReadSettings(config)
     -- called when loading new document
     self.location_stack = {}