InputContainer/FocusManager: Simplify key_events clearing on unplug

Thanks to @poire-z for the idea, it's indeed much nicer this way ;).

frontend/apps/reader/modules/readerpaging.lua

@@ -41,7 +41,7 @@ local ReaderPaging = InputContainer:extend{
 }
 
 function ReaderPaging:init()
-    self:registerKeyEvents(true)
+    self:registerKeyEvents()
     self.pan_interval = time.s(1 / self.pan_rate)
     self.number_of_pages = self.ui.document.info.number_of_pages
 
@@ -51,7 +51,7 @@ end
 
 function ReaderPaging:onGesture() end
 
-function ReaderPaging:registerKeyEvents(init)
+function ReaderPaging:registerKeyEvents()
     if Device:hasKeys() then
         self.key_events.GotoNextPage = {
             { { "RPgFwd", "LPgFwd", not Device:hasFewKeys() and "Right" } },
@@ -73,11 +73,6 @@ function ReaderPaging:registerKeyEvents(init)
             event = "GotoPosRel",
             args = -1,
         }
-    elseif not init then
-        self.key_events.GotoNextPage = nil
-        self.key_events.GotoPrevPage = nil
-        self.key_events.GotoNextPos = nil
-        self.key_events.GotoPrevPos = nil
     end
     if Device:hasKeyboard() then
         self.key_events.GotoFirst = {
@@ -130,22 +125,10 @@ function ReaderPaging:registerKeyEvents(init)
             event = "GotoPercent",
             args = 100,
         }
-    elseif not init then
-        self.key_events.GotoFirst = nil
-        self.key_events.Goto11 = nil
-        self.key_events.Goto22 = nil
-        self.key_events.Goto33 = nil
-        self.key_events.Goto44 = nil
-        self.key_events.Goto55 = nil
-        self.key_events.Goto66 = nil
-        self.key_events.Goto77 = nil
-        self.key_events.Goto88 = nil
-        self.key_events.GotoLast = nil
     end
 end
 
 ReaderPaging.onPhysicalKeyboardConnected = ReaderPaging.registerKeyEvents
-ReaderPaging.onPhysicalKeyboardDisconnected = ReaderPaging.registerKeyEvents
 
 function ReaderPaging:onReaderReady()
     self:setupTouchZones()