DB/Misc: removed manually set skinnable flag from all creatures as this flag is set during runtime

* added a missing trinity string

sql/updates/world/4.3.4/2020_07_14_01_world.sql

@@ -0,0 +1,7 @@
+-- Remove skinnable flag from all units
+UPDATE `creature_template` SET `unit_flags`= `unit_flags` &~ 67108864;
+
+-- Add missing trinity string
+DELETE FROM `trinity_string` WHERE `entry`= 1189;
+INSERT INTO `trinity_string` (`entry`, `content_default`) VALUES
+(1189, 'No instances were found matching your input.');