Remove PAGE_SIZE from <limits.h>.

It turns out that everyone's still getting PAGE_SIZE from <sys/user.h> via
<sys/ucontext.h> via <signal.h> anyway.

glibc has PAGE_SIZE in <sys/user.h> rather than <limits.h> so this part is
good. The bad part is that we have such wide transitive inclusion of
<sys/user.h>!

Bug: http://b/22735893
Change-Id: I363adffe4a27b4ca1eedf695ea621f5dd2d5ca10

libc/bionic/sysinfo.cpp

@@ -29,9 +29,9 @@
 #include <sys/sysinfo.h>
 
 #include <dirent.h>
-#include <limits.h>
 #include <stdio.h>
 #include <string.h>
+#include <unistd.h>
 
 #include "private/ScopedReaddir.h"
 
@@ -94,7 +94,7 @@ static int __get_meminfo_page_count(const char* pattern) {
   while (fgets(buf, sizeof(buf), fp) != NULL) {
     long total;
     if (sscanf(buf, pattern, &total) == 1) {
-      page_count = static_cast<int>(total / (PAGE_SIZE / 1024));
+      page_count = static_cast<int>(total / (sysconf(_SC_PAGE_SIZE) / 1024));
       break;
     }
   }

libc/include/limits.h

@@ -81,11 +81,6 @@
 
 #define MB_LEN_MAX 4
 
-/* New code should use sysconf(_SC_PAGE_SIZE) instead. */
-#ifndef PAGE_SIZE
-#define PAGE_SIZE 4096
-#endif
-
 #define SEM_VALUE_MAX 0x3fffffff
 
 /* POSIX says these belong in <unistd.h> but BSD has some in <limits.h>. */