remove a duplicated include

Detection of string_view type (whether it's std or Abseil)
is done in googletest/include/gtest/internal/gtest-port.h
with GTEST_INTERNAL_HAS_STRING_VIEW.

googletest/include/gtest/gtest-printers.h

@@ -111,10 +111,6 @@
 #include "gtest/internal/gtest-internal.h"
 #include "gtest/internal/gtest-port.h"
 
-#if GTEST_HAS_ABSL
-#include "absl/strings/string_view.h"
-#endif  // GTEST_HAS_ABSL
-
 namespace testing {
 
 // Definitions in the internal* namespaces are subject to change without notice.