Remove option SLOW_WAR

SLOW_WAR has issues:

* The check whether the attacker old-owns the attacked sector is
  broken, because att_abort() uses sect.sct_oldown uninitialized.

  Spotted by the Clang Static Analyzer.

* Its implementation in setrel() is somewhat scary.  It's actually
  okay, because that part of setrel() only runs within decl().  Other
  callers don't reach it: update_main() because player->god != 0
  there, and the rest because they never pass a rel < HOSTILE.

* Documentation is a bit vague.

SLOW_WAR hasn't been used in a public game in years.  Fixing it is not
worth it, so remove it instead.

src/lib/global/constants.c

@@ -191,9 +191,6 @@ double buil_tower_bt = 100.0;	/* tech level required to build a tower */
 int buil_tower_bh = 400;	/* hcm required to build a bridge tower */
 double buil_tower_bc = 3000.0;	/* cash required to build a bridge tower */
 
-/* opt_SLOW_WAR */
-int War_Cost = 1000;		/* Cost to declare war */
-
 float drnuke_const = 0.0;	/* research must be at least drnuke_const*tech */
 				/* in order to build a nuke. For example, if
 				 * drnuke_const is .25, you need a 75 res to

src/lib/global/options.c

@@ -59,7 +59,6 @@ int opt_NO_PLAGUE = 1;
 int opt_RAILWAYS = 1;
 int opt_RES_POP = 0;
 int opt_SAIL = 1;
-int opt_SLOW_WAR = 0;
 int opt_SUPER_BARS = 0;
 int opt_TECH_POP = 0;
 int opt_TRADESHIPS = 0;

src/lib/global/symbol.c

@@ -139,8 +139,6 @@ struct symbol nation_rejects[] = {
 struct symbol nation_relations[] = {
     {-1, "unknown"},
     {AT_WAR, "at-war"},
-    {SITZKRIEG, "sitzkrieg"},
-    {MOBILIZATION, "mobilization"},
     {HOSTILE, "hostile"},
     {NEUTRAL, "neutral"},
     {FRIENDLY, "friendly"},