Fixed typos and logic error in UnitFrame:Disable

This function is currently unused so these changes are not tested. The
Disable function now always hides the UnitFrame and calls
UnregisterUnitWatch with the correct parameters.

src/types/unitframe.lua

@@ -389,10 +389,9 @@ function UnitFrame:Disable()
     if self.hideInRaid then
         UnregisterAttributeDriver(self.secureFrame, "state-visibility")
     elseif self.unit ~= "player" then
-        UnregisterUnitWatch(self.secure_frame, self.condition)
-    else
-        self.secureFrame:Hide()
+        UnregisterUnitWatch(self.secureFrame, false)
     end
+    self.secureFrame:Hide()
 end
 
 -- returns true if this unit is a target unit