hsts: remove unused defines

MAX_HSTS_SUBLEN and MAX_HSTS_SUBLENSTR were unused from the initial commit,
and mostly likely leftovers from early development.  Remove as they're not
used for anything.

Closes #6741
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

lib/hsts.c

@@ -46,8 +46,6 @@
 #define MAX_HSTS_LINE 4095
 #define MAX_HSTS_HOSTLEN 256
 #define MAX_HSTS_HOSTLENSTR "256"
-#define MAX_HSTS_SUBLEN 4
-#define MAX_HSTS_SUBLENSTR "4"
 #define MAX_HSTS_DATELEN 64
 #define MAX_HSTS_DATELENSTR "64"