refactor: rollback utf8 validation

Author: proost

NOTICE

@@ -10,6 +10,3 @@ The Apache Software Foundation (http://www.apache.org/).
 
 Prior to moving to ASF, the software for this project was developed at
 Yahoo Inc. (https://developer.yahoo.com).
-
-This product includes utf8cpp (https://github.com/nemtrif/utfcpp),
-licensed under the Boost Software License, Version 1.0.

common/CMakeLists.txt

@@ -51,14 +51,3 @@ install(FILES
       include/serde.hpp
       include/xxhash64.h
   DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/DataSketches")
-
-install(FILES
-      include/third_party/utf8cpp/utf8.h
-      include/third_party/utf8cpp/utf8/checked.h
-      include/third_party/utf8cpp/utf8/core.h
-      include/third_party/utf8cpp/utf8/cpp11.h
-      include/third_party/utf8cpp/utf8/cpp17.h
-      include/third_party/utf8cpp/utf8/cpp20.h
-      include/third_party/utf8cpp/utf8/unchecked.h
-      include/third_party/utf8cpp/LICENSE
-  DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/DataSketches/third_party/utf8cpp")