Get rid of lkmc_assert_fail in favor of abort + assert

What was missing previously was implementing abort in baremetal.

I had done that previously and forgotten to do this conversion!

lkmc/add.c

@@ -1,4 +1,4 @@
-#include <lkmc.h>
+#include <assert.h>
 
 int main(void) {
     int i, j, k;
@@ -9,5 +9,5 @@ int main(void) {
     k = i + j;
     /* test-gdb-result */
     if (k != 3)
-        lkmc_assert_fail();
+        assert(0);
 }

lkmc/lkmc_assert_fail.c

@@ -1,5 +0,0 @@
-#include <lkmc.h>
-
-int main(void) {
-    lkmc_assert_fail();
-}