Remove use of AM_C_PROTOTYPES to fix autoreconf

The AM_C_PROTOTYPES macro no longer exists since automake 1.12. It
existed to support de-ANSI-fication of code using ansi2knr. It was
simply removed from coreutils m4/jm-macros.m4 in commit
88873501cff9ed937edf969cedd693517ab0a293, but this change was not
propagated to dc3dd, causing an autoreconf failure:

configure.ac:45: error: automatic de-ANSI-fication support has been removed
/home/peko/autobuild/instance-0/output/host/usr/share/aclocal-1.15/obsolete.m4:26: AM_C_PROTOTYPES is expanded from...
m4/jm-macros.m4:124: gl_CHECK_ALL_TYPES is expanded from...
m4/jm-macros.m4:22: coreutils_MACROS is expanded from...
configure.ac:45: the top level

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: b/m4/jm-macros.m4
===================================================================
--- a/m4/jm-macros.m4
+++ b/m4/jm-macros.m4
@@ -128,11 +128,6 @@
   dnl whether functions and headers are available, whether they work, etc.
   AC_REQUIRE([AC_SYS_LARGEFILE])
 
-  dnl This test must precede tests of compiler characteristics like
-  dnl that for the inline keyword, since it may change the degree to
-  dnl which the compiler supports such features.
-  AC_REQUIRE([AM_C_PROTOTYPES])
-
   dnl Checks for typedefs, structures, and compiler characteristics.
   AC_REQUIRE([AC_C_BIGENDIAN])
   AC_REQUIRE([AC_C_VOLATILE])