patch: delete legacy code

SoftwareSpec#add_legacy_patches and Patch#normalize_legacy_patches
were added almost 6 years ago; let's delete them

See commit 665b14c4a44c272b46b8559836e9fdbeee5d8a46

```
$ grep -r 'normalize_legacy_patches' Library/Homebrew
./software_spec.rb:    list = Patch.normalize_legacy_patches(list)
./patch.rb:  def self.normalize_legacy_patches(list)
```

```
$ grep -r 'add_legacy_patches' Library/Homebrew
./software_spec.rb:  def add_legacy_patches(list)
```

Library/Homebrew/patch.rb

@@ -29,25 +29,6 @@ module Patch
       raise ArgumentError, "unexpected value #{strip.inspect} for strip"
     end
   end
-
-  def self.normalize_legacy_patches(list)
-    patches = []
-
-    case list
-    when Hash
-      list
-    when Array, String, :DATA
-      { p1: list }
-    else
-      {}
-    end.each_pair do |strip, urls|
-      Array(urls).each do
-        patches << DATAPatch.new(strip)
-      end
-    end
-
-    patches
-  end
 end
 
 # An abstract class representing a patch embedded into a formula.

Library/Homebrew/software_spec.rb

@@ -227,13 +227,6 @@ class SoftwareSpec
     end
   end
 
-  # TODO: ?
-  def add_legacy_patches(list)
-    list = Patch.normalize_legacy_patches(list)
-    list.each { |p| p.owner = self }
-    patches.concat(list)
-  end
-
   def add_dep_option(dep)
     dep.option_names.each do |name|
       if dep.optional? && !option_defined?("with-#{name}")