nptl: Move pthread_atfork compatibility symbol to libc

The symbol was moved using scripts/move-symbol-to-libc.py.

There is no new symbol version because of the compatibility symbol
status.  The __pthread_atfork reference in nptl/Versions was unused.

sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist

@@ -850,6 +850,7 @@ GLIBC_2.0 program_invocation_name D 0x4
 GLIBC_2.0 program_invocation_short_name D 0x4
 GLIBC_2.0 pselect F
 GLIBC_2.0 psignal F
+GLIBC_2.0 pthread_atfork F
 GLIBC_2.0 pthread_attr_destroy F
 GLIBC_2.0 pthread_attr_getdetachstate F
 GLIBC_2.0 pthread_attr_getinheritsched F

sysdeps/unix/sysv/linux/sparc/sparc32/libpthread.abilist

@@ -10,7 +10,6 @@ GLIBC_2.0 __pthread_mutexattr_settype F
 GLIBC_2.0 flockfile F
 GLIBC_2.0 ftrylockfile F
 GLIBC_2.0 funlockfile F
-GLIBC_2.0 pthread_atfork F
 GLIBC_2.0 pthread_cancel F
 GLIBC_2.0 pthread_create F
 GLIBC_2.0 pthread_detach F

sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist

@@ -1306,6 +1306,7 @@ GLIBC_2.2 program_invocation_name D 0x8
 GLIBC_2.2 program_invocation_short_name D 0x8
 GLIBC_2.2 pselect F
 GLIBC_2.2 psignal F
+GLIBC_2.2 pthread_atfork F
 GLIBC_2.2 pthread_attr_destroy F
 GLIBC_2.2 pthread_attr_getdetachstate F
 GLIBC_2.2 pthread_attr_getinheritsched F

sysdeps/unix/sysv/linux/sparc/sparc64/libpthread.abilist

@@ -22,7 +22,6 @@ GLIBC_2.2 __res_state F
 GLIBC_2.2 flockfile F
 GLIBC_2.2 ftrylockfile F
 GLIBC_2.2 funlockfile F
-GLIBC_2.2 pthread_atfork F
 GLIBC_2.2 pthread_attr_getguardsize F
 GLIBC_2.2 pthread_attr_getstack F
 GLIBC_2.2 pthread_attr_getstackaddr F