Remove __ASSUME_PROC_PID_TASK_COMM.

This patch removes the __ASSUME_PROC_PID_TASK_COMM macro, and
associated conditional code (in a testcase), now that 3.2 is the
global minimum Linux kernel version supported.

Tested for x86_64.

	* sysdeps/unix/sysv/linux/kernel-features.h
	(__ASSUME_PROC_PID_TASK_COMM): Remove macro.
	* sysdeps/unix/sysv/linux/tst-setgetname.c: Do not include
	<kernel-features.h>.
	(do_test) [!__ASSUME_PROC_PID_TASK_COMM]: Remove conditional code.