Revert "arm64: add arm64_current_el to obtain current EL"

This reverts commit e38f2b2.

Author: xiaoxiang781216

arch/arm64/src/common/arm64_arch.h

@@ -394,26 +394,6 @@ static inline void arch_nop(void)
   __asm__ volatile ("nop");
 }
 
-/****************************************************************************
- * Name:
- *   arm64_current_el()
- *
- * Description:
- *
- *   Get current execution level
- *
- ****************************************************************************/
-
-#define arm64_current_el()                \
-  ({                                      \
-    uint64_t __el;                        \
-    int      __ret;                       \
-    __asm__ volatile ("mrs %0, CurrentEL" \
-                      : "=r" (__el));     \
-    __ret = GET_EL(__el);                 \
-    __ret;                                \
-  })
-
 /****************************************************************************
  * Name:
  *   read_/write_/zero_ sysreg