Remove vestigial de-ANSI-fication support.

configure.ac (AM_C_PROTOTYPES): Remove call to this macro.
The support for automatic de-ANSI-fication has been deprecated in
automake 1.11.2, and will be removed altogether in automake 1.12.0
diff --git a/configure.in b/configure.in
index 8d2153f..8183860 100644
--- a/configure.in
+++ b/configure.in
@@ -68,10 +68,6 @@
 AC_PATH_PROG(XMLLINT, xmllint, /usr/bin/xmllint)
 AC_PATH_PROG(XSLTPROC, xsltproc, /usr/bin/xsltproc)
 
-dnl Make sure we have an ANSI compiler
-AM_C_PROTOTYPES
-test "x$U" != "x" && AC_MSG_ERROR(Compiler not ANSI compliant)
-
 AC_LIBTOOL_WIN32_DLL
 AM_PROG_LIBTOOL