linux-user/loongarch64: Remove TARGET_FORCE_SHMLBA

The kernel abi was changed with

    commit d23b77953f5a4fbf94c05157b186aac2a247ae32
    Author: Huacai Chen <chenhuacai@kernel.org>
    Date:   Wed Jan 17 12:43:08 2024 +0800

        LoongArch: Change SHMLBA from SZ_64K to PAGE_SIZE

during the v6.8 cycle.

Reviewed-by: Song Gao <gaosong@loongson.cn>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

linux-user/loongarch64/target_syscall.h

@@ -38,11 +38,4 @@ struct target_pt_regs {
 #define TARGET_MCL_FUTURE  2
 #define TARGET_MCL_ONFAULT 4
 
-#define TARGET_FORCE_SHMLBA
-
-static inline abi_ulong target_shmlba(CPULoongArchState *env)
-{
-    return 64 * KiB;
-}
-
 #endif