remove some duplicates in bits/signum.h. No code changes.

remove some duplicates in bits/signum.h. No code changes.

 include/signal.h                        |   42 +++++++++++++++++++-------------
 libc/sysdeps/linux/alpha/bits/signum.h  |   19 --------------
 libc/sysdeps/linux/common/bits/signum.h |   22 ----------------
 libc/sysdeps/linux/hppa/bits/signum.h   |   17 ------------
 libc/sysdeps/linux/mips/bits/signum.h   |   23 +----------------
 libc/sysdeps/linux/sparc/bits/signum.h  |   20 ---------------
 6 files changed, 27 insertions(+), 116 deletions(-)