Revert "Also skip MFD_EXEC and MFD_NOEXEC_SEAL on sparc64"

This commit was included in [1] but was not present in the original
commmit. This was likely needed because of previous differences in CI
setup and MSRV between the two branches.

Now that the two branches are much more similar, the same kernel verion
and Rust versions are tested so this should no longer be needed.

This reverts commit 61331df.

[1]: rust-lang#3708

Author: tgross35

libc-test/build.rs

@@ -4126,10 +4126,7 @@ fn test_linux(target: &str) {
                 if ppc64 || riscv64 => true,
 
             // FIXME: requires more recent kernel headers on CI
-            | "MFD_EXEC"
-            | "MFD_NOEXEC_SEAL"
-            | "SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV"
-                if sparc64 => true,
+            "SECCOMP_FILTER_FLAG_WAIT_KILLABLE_RECV" if sparc64 => true,
 
             // FIXME: Not currently available in headers on ARM and musl.
             "NETLINK_GET_STRICT_CHK" if arm => true,