Remove obsolete macro REQUIRED_OPTION

Was used for the removed option 'terminal' and for 'font'. 'font' is no
longer this aggressive and doesn't use the macro.

Killing i3 when an option is missing would be super backwards
incompatible so I doubt we are going to use this ever again.

src/config.c

@@ -191,10 +191,6 @@ void load_configuration(xcb_connection_t *conn, const char *override_configpath,
 
     bindings = default_mode->bindings;
 
-#define REQUIRED_OPTION(name) \
-    if (config.name == NULL)  \
-        die("You did not specify required configuration option " #name "\n");
-
     /* Clear the old config or initialize the data structure */
     memset(&config, 0, sizeof(config));