devshell.bbclass: fix double unbuffering

stdout is already unbuffered in bitbake code. Attempt to
do it again in devshell.bbclass causes this crash when
running devpyshell:
  File "scripts/oepydevshell-internal.py", line 29, in <module>
      pty = open(sys.argv[1], "w+b", 0)
  IOError: [Errno 13] Permission denied: '/dev/pts/6'

(From OE-Core rev: 875910451e1ce97d0c42b41b1140c8160ed1f40a)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/devshell.bbclass

@@ -65,7 +65,6 @@ def devpyshell(d):
         os.dup2(m, sys.stdout.fileno())
         os.dup2(m, sys.stderr.fileno())
 
-        sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
         sys.stdin = os.fdopen(sys.stdin.fileno(), 'r', 0)
 
         bb.utils.nonblockingfd(sys.stdout)