ccanlint: use traversal to trim tests we want to skip.

Rather than using a separate index of tetst to skip, make sure tests
we don't want to run are removed from the graph of tests to start
with.

This means that the "skip" field is only set when we fail a test (and
thus must be reset when we test the next module).

tools/ccanlint/Makefile

@@ -3,7 +3,6 @@ TEST_OBJS := $(TEST_CFILES:.c=.o)
 
 CORE_OBJS := \
 	ccan/asort/asort.o \
-	ccan/btree/btree.o \
 	ccan/dgraph/dgraph.o \
 	ccan/foreach/foreach.o \
 	ccan/grab_file/grab_file.o \

tools/ccanlint/ccanlint.h

@@ -116,8 +116,6 @@ struct ccanlint {
 	struct dgraph_node node;
 	/* Did we skip a dependency?  If so, must skip this, too. */
 	const char *skip;
-	/* Did we fail a dependency?  If so, skip and mark as fail. */
-	bool skip_fail;
 	/* Did the user want to keep these results? */
 	bool keep_results;
 	/* Have we already run this? */