Fold conv package into fmt

Both packages had nearly identical dependency requirements, so merging
them should help reduce the complexity of the build graph.

third_party/lemon/lemon.c

@@ -10,7 +10,7 @@
 #include "libc/alg/alg.h"
 #include "libc/assert.h"
 #include "libc/calls/calls.h"
-#include "libc/conv/conv.h"
+#include "libc/fmt/conv.h"
 #include "libc/fmt/fmt.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/gc.h"