system/core: preparation to pull back interfaces from android/log.h

Point to log/log.h where necessary, define LOG_TAG where necessary.
Accept that private/android_logger.h is suitable replacement for
log/logger.h and android/log.h.

Correct liblog/README

Effectively a cleanup and controlled select revert of
'system/core: drop or replace log/logger.h' and
'system/core: Replace log/log.h with android/log.h'.

Test: compile
Bug: 30465923
Change-Id: Ic2ad157bad6f5efe2c6af293a73bb753300b17a2
diff --git a/libutils/Unicode.cpp b/libutils/Unicode.cpp
index 0652101..c32f462 100644
--- a/libutils/Unicode.cpp
+++ b/libutils/Unicode.cpp
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#define LOG_TAG "unicode"
+
 #include <limits.h>
 #include <stddef.h>