Hatena: Do not initialize with extern.

Do not initialize with extern in header file.

>mingw32-g++ -Wall -O3 -o array_counter.o -c array_counter.cpp
In file included from array_counter.cpp:5:0:
array_counter.h:14:14: warning: 'char_line_end' initialized and declared 'extern'
 extern char* char_line_end = (char*) "\r\n";
              ^~~~~~~~~~~~~
array_counter.cpp:7:7: error: redefinition of 'char* char_line_end'
char* char_line_end = (char*)"\r\n";

===array_counter.cpp ===
char* char_line_end = (char*)"\r\n";

=== array_counter.h ===
// Here, we must use the below at 20190304.
// extern char* char_line_end;
extern char* char_line_end = (char*) "\r\n";