iwyu: ignore `std::remove_reference` requirements

This removes some includes from some existing files.

Source/cmCMakeHostSystemInformationCommand.cxx

@@ -8,7 +8,6 @@
 #include <initializer_list>
 #include <map>
 #include <string>
-#include <type_traits>
 #include <utility>
 
 #include <cm/optional>

Source/cmString.cxx

@@ -9,7 +9,6 @@
 #include <ostream>
 #include <stdexcept>
 #include <string>
-#include <type_traits>
 
 namespace cm {
 

Tests/CMakeLib/testStringAlgorithms.cxx

@@ -1,12 +1,11 @@
 /* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
    file Copyright.txt or https://cmake.org/licensing for details.  */
 
-#include <cmConfigure.h> // IWYU pragma: keep
+#include "cmConfigure.h" // IWYU pragma: keep
 
 #include <iostream>
 #include <sstream>
 #include <string>
-#include <type_traits>
 #include <utility>
 #include <vector>
 

Utilities/IWYU/mapping.imp

@@ -99,6 +99,7 @@
   { symbol: [ "std::enable_if<true, std::chrono::duration<long, std::ratio<60, 1> > >::type", private, "\"cmConfigure.h\"", public ] },
   { symbol: [ "std::enable_if<true, std::chrono::duration<long, std::ratio<1, 1000> > >::type", private, "\"cmConfigure.h\"", public ] },
   { symbol: [ "__gnu_cxx::__enable_if<true, bool>::__type", private, "\"cmConfigure.h\"", public ] },
+  { symbol: [ "std::remove_reference<std::basic_string<char, std::char_traits<char>, std::allocator<char> > &>::type", private, "\"cmConfigure.h\"", public ] },
   { symbol: [ "std::remove_reference<Defer &>::type", private, "\"cmConfigure.h\"", public ] },
 
   # Wrappers for 3rd-party libraries