Remove redundant extern variable lcd_encoder from menu.cpp

This extern variable is included from lcd.h

Firmware/menu.cpp

@@ -14,8 +14,6 @@
 #include "static_assert.h"
 #include "sound.h"
 
-extern int32_t lcd_encoder;
-
 #define MENU_DEPTH_MAX       7
 
 static menu_record_t menu_stack[MENU_DEPTH_MAX];