[FIX] web: allow standard shortcuts on firefox

when navigating with the keyboard, using the ALT key is the trigger
for most of the access keys. In Firefox on Linux, this prevents a number
of existing shortcuts (like ALT+Left arrow for browser back).

This fix allows browsers to execute those shortcuts.

Note: in Firefox on linux ALT+F E V S B T H are assigned to menus and
cannot be stopped, removing the keypress handler does not change
anything.

addons/web/static/src/js/chrome/keyboard_navigation_mixin.js

@@ -26,7 +26,6 @@ odoo.define('web.KeyboardNavigationMixin', function (require) {
     var KeyboardNavigationMixin = {
         events: {
             'keydown': '_onKeyDown',
-            'keypress': '_onKeyPress',
             'keyup': '_onKeyUp',
         },
 
@@ -177,21 +176,6 @@ odoo.define('web.KeyboardNavigationMixin', function (require) {
                 }
             }
         },
-        /**
-         * hides the shortcut overlays when key press event is triggered on the ALT key
-         *
-         * @private
-         * @param keyPressEvent {jQueryKeyboardEvent} the keyboard event triggered
-         * @return {undefined|false}
-         */
-        _onKeyPress: function (keyPressEvent) {
-            if ((keyPressEvent.altKey || keyPressEvent.key === 'Alt') && !keyPressEvent.ctrlKey) {
-                if (keyPressEvent.preventDefault) keyPressEvent.preventDefault(); else keyPressEvent.returnValue = false;
-                if (keyPressEvent.stopPropagation) keyPressEvent.stopPropagation();
-                if (keyPressEvent.cancelBubble) keyPressEvent.cancelBubble = true;
-                return false;
-            }
-        },
         /**
          * hides the shortcut overlays when keyup event is triggered on the ALT key
          *