libutils: Cleanup unused class declaration

This commit removes unused class declaration for SharedBuffer and
TextOutput.  SharedBuffer has become internal implementation details
since 282efae9c.  TextOutput usages have been removed since 9eb2a3b1.

Test: AOSP and master build w/o problems
Change-Id: I1871c4919a46f1ea8f41fb7eb79b4dc800b6f6f4
diff --git a/libutils/include/utils/String16.h b/libutils/include/utils/String16.h
index cb3d338..15ed19f 100644
--- a/libutils/include/utils/String16.h
+++ b/libutils/include/utils/String16.h
@@ -35,9 +35,7 @@
 
 // ---------------------------------------------------------------------------
 
-class SharedBuffer;
 class String8;
-class TextOutput;
 
 //! This is a string holding UTF-16 characters.
 class String16
diff --git a/libutils/include/utils/String8.h b/libutils/include/utils/String8.h
index 1f3e5d8..0225c6b 100644
--- a/libutils/include/utils/String8.h
+++ b/libutils/include/utils/String8.h
@@ -31,7 +31,6 @@
 namespace android {
 
 class String16;
-class TextOutput;
 
 //! This is a string holding UTF-8 characters. Does not allow the value more
 // than 0x10FFFF, which is not valid unicode codepoint.