Remove the hat of the High Council

It's one of a very large number of mechanically similar unrands that improve
spellcasting in some way at a cost (robe of Folly, hat of Pondering, Majin-Bo,
Maxwell's Etheric Cage) and probably has the least interesting downside
of them (and orange crystal plate is also similar in practice, since it has
Archmagi but reduces success by virtue of being CPA).

crawl-ref/source/art-data.txt

@@ -1114,6 +1114,7 @@ BASE_DAM: +35
 BASE_DELAY: +13
 BRAND:    SPWPN_VORPAL
 
+# TAG_MAJOR_VERSION == 34
 ENUM:    HIGH_COUNCIL
 NAME:    hat of the High Council
 INSCRIP: Wiz-
@@ -1124,6 +1125,7 @@ TILE_EQ: wizard_lightgreen
 PLUS:    +2
 BRAND:   SPARM_ARCHMAGI
 STEALTH: -1
+BOOL:    nogen
 
 NAME:     arc blade
 INSCRIP:  discharge,

crawl-ref/source/dat/descript/unrand.txt

@@ -540,6 +540,7 @@ A large, iron-shod maul specialised for dealing massively powerful blows. Such
 power comes at a price: the maul's head is so heavy it takes a great length of
 time to lift it up for another swing.
 %%%%
+# TAG_MAJOR_VERSION == 34
 hat of the High Council
 
 A relic of some ancient wizarding war. Centuries later, it still crackles with

crawl-ref/source/spl-cast.cc

@@ -385,9 +385,6 @@ int raw_spell_fail(spell_type spell)
     chance2 += 4 * player_mutation_level(MUT_WILD_MAGIC);
     chance2 += 4 * player_mutation_level(MUT_ANTI_WIZARDRY);
 
-    if (player_equip_unrand(UNRAND_HIGH_COUNCIL))
-        chance2 += 7;
-
     if (you.props.exists(SAP_MAGIC_KEY))
         chance2 += you.props[SAP_MAGIC_KEY].get_int() * 12;