procfs: simplify conditional processing of fs/proc.o.

Since the entire fs/proc directory is conditionally included based on
CONFIG_PROC_FS, it's redundant to check that same variable within that
directory.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>