Makefile: do not use check_config

test(1) only uses the second to compare two files dates.
test(1) also does a strict comparison wrt. dates.

But, on very fast systems, the configure and .config.mk
files may be created in the same second, and so would lead
to a false comparison of the files' dates.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

diff -durN tvheadend-v3.5.orig/Makefile tvheadend-v3.5/Makefile
--- tvheadend-v3.5.orig/Makefile	2013-02-17 15:15:03.228749505 +0100
+++ tvheadend-v3.5/Makefile	2013-02-17 15:15:51.591923062 +0100
@@ -250,7 +250,7 @@
 	$(ROOTDIR)/configure $(CONFIGURE_ARGS)
 
 # Binary
-${PROG}: check_config $(OBJS) $(ALLDEPS)
+${PROG}: $(OBJS) $(ALLDEPS)
 	$(CC) -o $@ $(OBJS) $(CFLAGS) $(LDFLAGS)
 
 # Object