SQLite does not depend on zlib

Fixes build error when zlib target package is not present:
/home/br/br2/output/host/opt/ext-toolchain/bin/../lib/gcc/arm-linux-gnueabihf/4.9.2/../../../../arm-linux-gnueabihf/bin/ld: cannot find -lz

Patch for configure.ac sent upstream:
http://www.dovecot.org/list/dovecot/2014-November/098634.html

Here we patch ./configure instead because autoreconf is broken.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>

diff -uNr dovecot-2.2.15.org/configure dovecot-2.2.15/configure
--- dovecot-2.2.15.org/configure	2014-10-25 06:08:57.000000000 +0200
+++ dovecot-2.2.15/configure	2014-11-08 10:08:53.430745198 +0100
@@ -23865,7 +23865,7 @@
 		ac_fn_c_check_header_mongrel "$LINENO" "sqlite3.h" "ac_cv_header_sqlite3_h" "$ac_includes_default"
 if test "x$ac_cv_header_sqlite3_h" = xyes; then :
 
-			SQLITE_LIBS="$SQLITE_LIBS -lsqlite3 -lz"
+			SQLITE_LIBS="$SQLITE_LIBS -lsqlite3"
 
 
 $as_echo "#define HAVE_SQLITE /**/" >>confdefs.h