This is checked by configure and passed as a define directive when building.
There's no need to check again and potentially override a failed check
(uClibc <= 0.9.33.2 for example lacks posix_fallocate).

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura sqlite-autoconf-3071700.orig/sqlite3.c sqlite-autoconf-3071700/sqlite3.c
--- sqlite-autoconf-3071700.orig/sqlite3.c	2013-05-23 03:17:27.170459400 -0300
+++ sqlite-autoconf-3071700/sqlite3.c	2013-05-23 03:25:01.839227616 -0300
@@ -22931,13 +22931,6 @@
 */
 #if SQLITE_OS_UNIX              /* This file is used on unix only */

-/* Use posix_fallocate() if it is available
-*/
-#if !defined(HAVE_POSIX_FALLOCATE) \
-      && (_XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L)
-# define HAVE_POSIX_FALLOCATE 1
-#endif
-
 /*
 ** There are various methods for file locking used for concurrency
 ** control: