[arch][arm64] remove an unnecessary call to arm64_el3_to_el1

The existing arm64_elx_to_el1 already handles dropping the primary and
any secondary cpu down to el1 by the time this code path is reached.

arch/arm64/arch.c

@@ -31,12 +31,6 @@ static void arm64_cpu_early_init(void) {
     /* set the vector base */
     ARM64_WRITE_SYSREG(VBAR_EL1, (uint64_t)&arm64_exception_base);
 
-    /* switch to EL1 */
-    unsigned int current_el = ARM64_READ_SYSREG(CURRENTEL) >> 2;
-    if (current_el > 1) {
-        arm64_el3_to_el1();
-    }
-
     arch_enable_fiqs();
 }