uninstall: load formula from rack

Closes Homebrew/homebrew#39524.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/cmd/uninstall.rb

@@ -11,9 +11,8 @@ module Homebrew
           puts "Uninstalling #{keg}... (#{keg.abv})"
           keg.unlink
           keg.uninstall
-          rm_pin keg.name
+          rack = keg.rack
-
+          rm_pin rack
-          rack = keg/".."
           if rack.directory?
             versions = rack.subdirs.map(&:basename)
             verb = versions.length == 1 ? "is" : "are"
@@ -36,7 +35,7 @@ module Homebrew
           end
         end
 
-        rm_pin name
+        rm_pin rack
       end
     end
   rescue MultipleVersionsInstalledError => e
@@ -44,7 +43,7 @@ module Homebrew
     puts "Use `brew remove --force #{e.name}` to remove all versions."
   end
 
-  def rm_pin name
+  def rm_pin rack
-    Formulary.factory(name).unpin rescue nil
+    Formulary.from_rack(rack).unpin rescue nil
   end
 end