Fold conv package into fmt

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

dsp/mpeg/mpeg1.c

@@ -33,7 +33,7 @@
 #include "dsp/mpeg/mpeg.h"
 #include "dsp/mpeg/video.h"
 #include "libc/bits/initializer.internal.h"
-#include "libc/conv/conv.h"
+#include "libc/fmt/conv.h"
 #include "libc/log/log.h"
 #include "libc/macros.h"
 #include "libc/math.h"