Remove unused Tooltip#validate method

js/tooltip.js

@@ -407,14 +407,6 @@
     return (this.$arrow = this.$arrow || this.tip().find('.tooltip-arrow'))
   }
 
-  Tooltip.prototype.validate = function () {
-    if (!this.$element[0].parentNode) {
-      this.hide()
-      this.$element = null
-      this.options  = null
-    }
-  }
-
   Tooltip.prototype.enable = function () {
     this.enabled = true
   }