refactor: remove regex related cmake stuff

cmake/config.h.cmake

@@ -35,9 +35,6 @@
 #define EXV_ICONV_CONST
 #endif
 
-// Define if you have the <regex.h> header file.
-#cmakedefine EXV_HAVE_REGEX_H
-
 // Define if you have the mmap function.
 #cmakedefine EXV_HAVE_MMAP
 

cmake/generateConfigFile.cmake

@@ -39,7 +39,6 @@ int main() {
 check_include_file_cxx( "unistd.h"      EXV_HAVE_UNISTD_H )
 check_include_file_cxx( "sys/mman.h"    EXV_HAVE_SYS_MMAN_H )
 if ( NOT MINGW AND NOT MSYS AND NOT MSVC )
-check_include_file_cxx( "regex.h"       EXV_HAVE_REGEX_H )
 endif()
 
 set(EXV_ENABLE_NLS ${EXIV2_ENABLE_NLS})