Remove commit#to_diff and commit#to_patch

These methods will be unused when gitlab-org/gitlab-ce!5367 is merged,
therefor not needed here.

CHANGELOG

+v 10.5.0 (unreleased)
+  - Remove commit#to_diff and commit#to_patch
+
 v 10.4.0
   - Move implementation of `local_branches` to `Gitlab::Git::Repository` from gitlab-ce
   - Refactor Refs to preserve their target objects instead of just a string representation

lib/gitlab_git/commit.rb

@@ -175,13 +175,6 @@ module Gitlab
         parent_ids.first
       end
-      # Shows the diff between the commit's parent and the commit.
-      #
-      # Cuts out the header and stats from #to_patch and returns only the diff.
-      def to_diff(options = {})
-        diff_from_parent(options).patch
-      end
-
       # Returns a diff object for the changes from this commit's first parent.
       # If there is no parent, then the diff is between this commit and an
       # empty repo.  See Repository#diff for keys allowed in the +options+
@@ -226,16 +219,6 @@ module Gitlab
         Gitlab::Git::CommitStats.new(self)
       end
-      def to_patch(options = {})
-        begin
-          raw_commit.to_mbox(options)
-        rescue Rugged::InvalidError => ex
-          if ex.message =~ /Commit \w+ is a merge commit/
-            'Patch format is not currently supported for merge commits.'
-          end
-        end
-      end
-
       # Get a collection of Rugged::Reference objects for this commit.
       #
       # Ex.

spec/commit_spec.rb

@@ -336,24 +336,10 @@ describe Gitlab::Git::Commit do
     end
   end
-  describe :to_diff do
-    subject { commit.to_diff }
-
-    it { is_expected.not_to include "From #{SeedRepo::Commit::ID}" }
-    it { is_expected.to include 'diff --git a/files/ruby/popen.rb b/files/ruby/popen.rb'}
-  end
-
   describe :has_zero_stats? do
     it { expect(commit.has_zero_stats?).to eq(false) }
   end
-  describe :to_patch do
-    subject { commit.to_patch }
-
-    it { is_expected.to include "From #{SeedRepo::Commit::ID}" }
-    it { is_expected.to include 'diff --git a/files/ruby/popen.rb b/files/ruby/popen.rb'}
-  end
-
   describe :to_hash do
     let(:hash) { commit.to_hash }
     subject { hash }