Remove ShowFontMenu (#11904)

Some clean up, as suggested in <https://github.com/koreader/koreader/pull/11864#discussion_r1615312993>.

frontend/apps/reader/modules/readerfont.lua

@@ -1,5 +1,4 @@
 local BD = require("ui/bidi")
-local CenterContainer = require("ui/widget/container/centercontainer")
 local ConfirmBox = require("ui/widget/confirmbox")
 local Device = require("device")
 local Event = require("ui/event")
@@ -8,7 +7,6 @@ local FontList = require("fontlist")
 local InfoMessage = require("ui/widget/infomessage")
 local Input = Device.input
 local InputContainer = require("ui/widget/container/inputcontainer")
-local Menu = require("ui/widget/menu")
 local MultiConfirmBox = require("ui/widget/multiconfirmbox")
 local Notification = require("ui/widget/notification")
 local Screen = require("device").screen
@@ -142,7 +140,6 @@ function ReaderFont:onGesture() end
 
 function ReaderFont:registerKeyEvents()
     if Device:hasKeyboard() then
-        self.key_events.ShowFontMenu = { { "F" } }
         if not (Device:hasScreenKB() or Device:hasSymKey()) then
             -- add shortcut for keyboard
             self.key_events.IncreaseSize = {
@@ -196,34 +193,6 @@ function ReaderFont:onReadSettings(config)
     end)
 end
 
-function ReaderFont:onShowFontMenu()
-    -- build menu widget
-    local main_menu = Menu:new{
-        title = self.font_menu_title,
-        item_table = self.face_table,
-        width = Screen:getWidth() - 100,
-        height = math.floor(Screen:getHeight() * 0.5),
-        single_line = true,
-        items_per_page = 8,
-        items_font_size = Menu.getItemFontSize(8),
-    }
-    -- build container
-    local menu_container = CenterContainer:new{
-        dimen = Screen:getSize(),
-        main_menu,
-    }
-    main_menu.close_callback = function()
-        UIManager:close(menu_container)
-    end
-    -- show menu
-
-    main_menu.show_parent = menu_container
-
-    UIManager:show(menu_container)
-
-    return true
-end
-
 --[[
     UpdatePos event is used to tell ReaderRolling to update pos.
 --]]