build: LT_INIT already replaces AC_PROG_LIBTOOL.

Signed-off-by: Diego Elio Pettenò <flameeyes@flameeyes.eu>
diff --git a/configure.ac b/configure.ac
index deb5fd4..b0c0fb7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -14,7 +14,6 @@
 AC_PROG_CC
 AC_PROG_INSTALL
 LT_INIT
-AC_PROG_LIBTOOL
 
 AC_CONFIG_MACRO_DIR([m4])