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/readerpanning.lua

@@ -38,8 +38,12 @@ function ReaderPanning:init()
             },
         }
     end
+    -- NOP our own gesture handling
+    self.ges_events = nil
 end
 
+function ReaderPanning:onGesture() end
+
 function ReaderPanning:onSetDimensions(dimensions)
     self.dimen = dimensions
 end