The __ASSUME_SOCKETCALL macro in kernel-features.h is no longer used
for anything. (It used to be used in defining other macros related to
accept4 / recvmmsg / sendmmsg availability, but the code in that area
was simplified once we could assume a kernel with those features,
whether through a syscall or through socketcall, so allowing those
functions to be handled much like other socket operations, without
requring __ASSUME_SOCKETCALL.) This patch removes that unused macro.
(Note: once we can assume a Linux 4.4 or later kernel, much of the
support for using socketcall at all can be removed from glibc,
although a few functions may need that support in glibc for longer.)