Revert "kunit: move string-stream.h to lib/kunit"

This reverts commit 109fb06.

string-stream will be used by kunit mocking code to print messages about
mock expectations.
It makes the code signifcantly simpler if string-stream objects can be
part of structs declared in mocking headers.

Signed-off-by: Daniel Latypov <dlatypov@google.com>

include/kunit/assert.h

@@ -9,11 +9,10 @@
 #ifndef _KUNIT_ASSERT_H
 #define _KUNIT_ASSERT_H
 
+#include <kunit/string-stream.h>
 #include <linux/err.h>
-#include <linux/kernel.h>
 
 struct kunit;
-struct string_stream;
 
 /**
  * enum kunit_assert_type - Type of expectation/assertion.

lib/kunit/assert.c

@@ -8,8 +8,6 @@
 #include <kunit/assert.h>
 #include <kunit/test.h>
 
-#include "string-stream.h"
-
 void kunit_base_assert_format(const struct kunit_assert *assert,
 			      struct string_stream *stream)
 {

lib/kunit/string-stream-test.c

@@ -6,11 +6,10 @@
  * Author: Brendan Higgins <brendanhiggins@google.com>
  */
 
+#include <kunit/string-stream.h>
 #include <kunit/test.h>
 #include <linux/slab.h>
 
-#include "string-stream.h"
-
 static void string_stream_test_empty_on_creation(struct kunit *test)
 {
 	struct string_stream *stream = alloc_string_stream(test, GFP_KERNEL);

lib/kunit/string-stream.c

@@ -6,12 +6,11 @@
  * Author: Brendan Higgins <brendanhiggins@google.com>
  */
 
+#include <kunit/string-stream.h>
 #include <kunit/test.h>
 #include <linux/list.h>
 #include <linux/slab.h>
 
-#include "string-stream.h"
-
 struct string_stream_fragment_alloc_context {
 	struct kunit *test;
 	int len;

lib/kunit/test.c

@@ -7,12 +7,12 @@
  */
 
 #include <kunit/test.h>
+#include <kunit/string-stream.h>
 #include <linux/kernel.h>
 #include <linux/kref.h>
 #include <linux/sched/debug.h>
 
 #include "debugfs.h"
-#include "string-stream.h"
 #include "try-catch-impl.h"
 
 static void kunit_set_failure(struct kunit *test)