gdb: syscalls: Remove tips for LoongArch xml files

After commit "gdb: syscalls: Handle __NR3264_ prefixed syscall number",
no need to do special handling when generating xml file for LoongArch,
just remove the tips in the file comment.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Approved-By: Tom de Vries <tdevries@suse.de>