[kernel] Move the logger from kutil into kernel

Part one of a series of code moves. The kutil library is not very
useful, as most of its code is kernel-specific. This was originally for
testing purposes, but that can be achieved in other ways with the
current build system. I find this mostly creates a strange division in
the kernel code.

Instead, I'm going to move everything kernel-specific to actually be in
the kernel, and replace kutil with just 'util' for generic utility code
I want to share.

This commit:

- Moves the logger into the kernel.
- Updates the 'printf' library used from mpaland/printf to
  eyalroz/printf and moved it into the kernel, as it's only used by the
  logger in kutil.
- Removes some other unused kutil headers from some files, to help
  future code rearrangement.

Note that the (now redundant-seeming) log.cpp/h in kernel is currently
still there - these files are more about log output than the logging
system, and will get replaced once I add user-space log output.

src/kernel/console.cpp

@@ -1,8 +1,6 @@
-#include "kutil/coord.h"
-#include "kutil/guid.h"
 #include "kutil/memory.h"
 #include "kutil/no_construct.h"
-#include "kutil/printf.h"
+#include "printf/printf.h"
 #include "console.h"
 #include "serial.h"
 
@@ -81,6 +79,6 @@ void console::vprintf(const char *fmt, va_list args)
 {
     static const unsigned buf_size = 256;
     char buffer[buf_size];
-    vsnprintf_(buffer, buf_size, fmt, args);
+    vsnprintf(buffer, buf_size, fmt, args);
     puts(buffer);
 }