selftests/futex: Remove unused test_futex_mpol()

selftests/futex: Remove unused test_futex_mpol()

Commit ed323aeda5e09 ("selftest/futex: Compile also with libnuma <
2.0.16") removed the unused function test_futex_mpol() and commit
d35ca2f64272 ("selftests/futex: Refactor futex_numa_mpol with
kselftest_harness.h") added it back by accident. Remove it again.

Fixes: d35ca2f64272 ("selftests/futex: Refactor futex_numa_mpol with kselftest_harness.h")
Signed-off-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251001220438.66227-1-andrealmeid@igalia.com