Get rid of string structures

These were only used to construct constant strings with additional
length fields. However, we can just use standard constant character
arrays instead and let the compiler calculate the string length.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/calcurse.h

@@ -210,7 +210,6 @@
     }                                                                         \
 } while (0)
 
-#define STRING_BUILD(str) {str, sizeof (str) - 1}
 #define STRINGIFY(x)  #x
 #define TOSTRING(x)   STRINGIFY(x)
 #define __FILE_POS__   __FILE__ ":" TOSTRING(__LINE__)
@@ -248,11 +247,6 @@ struct dmon_conf {
   unsigned  log;      /* log daemon activity */
 };
 
-struct string {
-  const char   *str;
-  const int     len;
-};
-
 enum datefmt {
   DATEFMT_MMDDYYYY = 1,
   DATEFMT_DDMMYYYY,