SkString: remove externally unused ::setUTF16() from API

Moved to SkStringUtils in src/

Change-Id: I026e3a325570bbf34e90797d921cb2f05b9a29f6
Reviewed-on: https://skia-review.googlesource.com/111602
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
diff --git a/src/core/SkStringUtils.h b/src/core/SkStringUtils.h
index fecf833..f2a1443 100644
--- a/src/core/SkStringUtils.h
+++ b/src/core/SkStringUtils.h
@@ -40,4 +40,6 @@
 /** Indents every non-empty line of the string by tabCnt tabs */
 SkString SkTabString(const SkString& string, int tabCnt);
 
+SkString SkStringFromUTF16(const uint16_t* src, size_t count);
+
 #endif