riscv: vmlinux-xip.lds.S: remove .alternative section

ALTERNATIVE mechanism can't work on XIP, and this is also reflected by
below Kconfig dependency:

RISCV_ALTERNATIVE
	...
	depends on !XIP_KERNEL
	...

So there's no .alternative section at all for XIP case, remove it.
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com> # build
Link: https://lore.kernel.org/r/20230523165502.2592-3-jszhang@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/kernel/vmlinux-xip.lds.S

@@ -98,12 +98,6 @@ SECTIONS
 		__soc_builtin_dtb_table_end = .;
 	}
 
-	. = ALIGN(8);
-	.alternative : {
-		__alt_start = .;
-		*(.alternative)
-		__alt_end = .;
-	}
 	__init_end = .;
 
 	. = ALIGN(16);