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-c84bc2b72b462ef2dbed305f3fd0bb3fa5046fc3.orig/Makefile tvheadend-c84bc2b72b462ef2dbed305f3fd0bb3fa5046fc3/Makefile
--- tvheadend-c84bc2b72b462ef2dbed305f3fd0bb3fa5046fc3.orig/Makefile	2014-03-09 14:47:43.780025330 +0100
+++ tvheadend-c84bc2b72b462ef2dbed305f3fd0bb3fa5046fc3/Makefile	2014-03-09 14:48:40.836539093 +0100
@@ -708,7 +708,7 @@
 	$(ROOTDIR)/configure $(CONFIGURE_ARGS)
 
 # Binary
-${PROG}: .config.mk make_webui $(OBJS)
+${PROG}: make_webui $(OBJS)
 	$(pCC) -o $@ $(OBJS) $(CFLAGS) $(LDFLAGS)
 
 # Object