selftests/bpf: Fix errors compiling cg_storage_multi.h with musl libc

Remove a redundant include of '<asm/types.h>', whose needed definitions are
already included (via '<linux/types.h>') in cg_storage_multi_egress_only.c,
cg_storage_multi_isolated.c, and cg_storage_multi_shared.c. This avoids
redefinition errors seen compiling for mips64el/musl-libc like:

  In file included from progs/cg_storage_multi_egress_only.c:13:
  In file included from progs/cg_storage_multi.h:6:
  In file included from /usr/mips64el-linux-gnuabi64/include/asm/types.h:23:
  /usr/include/asm-generic/int-l64.h:29:25: error: typedef redefinition with different types ('long' vs 'long long')
     29 | typedef __signed__ long __s64;
        |                         ^
  /usr/include/asm-generic/int-ll64.h:30:44: note: previous definition is here
     30 | __extension__ typedef __signed__ long long __s64;
        |                                            ^

Fixes: 9e5bd1f7 ("selftests/bpf: Test CGROUP_STORAGE map can't be used by multiple progs")
Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/4f4702e9f6115b7f84fea01b2326ca24c6df7ba8.1721713597.git.tony.ambardar@gmail.com

tools/testing/selftests/bpf/progs/cg_storage_multi.h

@@ -3,8 +3,6 @@
 #ifndef __PROGS_CG_STORAGE_MULTI_H
 #define __PROGS_CG_STORAGE_MULTI_H
 
-#include <asm/types.h>
-
 struct cgroup_value {
 	__u32 egress_pkts;
 	__u32 ingress_pkts;