Prevent using Nemelex and Ru abilities under silence

They were the only god invocations usable under silence, for flavour reasons
rather than gameplay ones, which mostly made them unintuitive exceptions.

crawl-ref/docs/changelog.txt

@@ -280,7 +280,6 @@ Gods
         destination. Inflicts medium exhaustion.
   - 5*: Apocalypse: Deals very high damage to all monsters in LOS and inflicts
         statuses. Inflicts heavy drain and exhaustion.
-  - Ru's abilities can be used while silenced.
 * All gods now treat followers' kills the same as the player's, for purposes of
   piety gain.
 * Makhleb and Okawaru no longer support corpse sacrifice.

crawl-ref/source/ability.cc

@@ -1515,8 +1515,7 @@ static bool _check_ability_possible(const ability_def& abil,
         return false;
     }
 
-    if (silenced(you.pos()) && !you_worship(GOD_NEMELEX_XOBEH)
-          && !you_worship(GOD_RU))
+    if (silenced(you.pos()))
     {
         talent tal = get_talent(abil.ability, false);
         if (tal.is_invocation)
@@ -3983,15 +3982,9 @@ vector<ability_type> get_god_abilities(bool include_unusable, bool ignore_piety)
     else if (you.transfer_skill_points > 0)
         abilities.push_back(ABIL_ASHENZARI_END_TRANSFER);
 
-    // Remaining abilities are unusable if under penance, or if silenced if not
-    // Nemelex abilities.
-    if (!include_unusable && (player_under_penance()
-                              || silenced(you.pos())
-                              && !you_worship(GOD_NEMELEX_XOBEH)
-                              && !you_worship(GOD_RU)))
-    {
+    // Remaining abilities are unusable if under penance, or if silenced.
+    if (!include_unusable && (player_under_penance() || silenced(you.pos())))
         return abilities;
-    }
 
     for (int i = 0; i < MAX_GOD_ABILITIES; ++i)
     {