buildsys: metag: Remove inappropriate comment

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libpthread/nptl/sysdeps/unix/sysv/linux/metag/Makefile.arch

@@ -29,6 +29,3 @@ CFLAGS-fork.c = -D__USE_STDIO_FUTEXES__
 endif
 CFLAGS-OMIT-fork.c = -DNOT_IN_libc -DIS_IN_libpthread
 CFLAGS-OMIT-libc-lowlevellock.c = -DNOT_IN_libc -DIS_IN_libpthread
-# We always compile it in arm mode because of SAVE_PID macro
-# This macro should be alternatively implemented in THUMB
-# assembly.