update: remove unused rename detection

Right now this code only produces false positives. When we have real
support for renames, we can implement it more carefully.

Closes Homebrew/homebrew#31126.

Library/Homebrew/cmd/update.rb

@@ -172,12 +172,8 @@ class Updater
     map = Hash.new{ |h,k| h[k] = [] }
 
     if initial_revision && initial_revision != current_revision
-      `git diff-tree -r --name-status -M85% #{initial_revision} #{current_revision}`.each_line do |line|
-        status, path, renamed = line.split
-        if renamed
-          status = status[0, 1]
-          path = renamed
-        end
+      `git diff-tree -r --name-status --diff-filter=AMD #{initial_revision} #{current_revision}`.each_line do |line|
+        status, path = line.split
         map[status.to_sym] << repository.join(path)
       end
     end
@@ -226,7 +222,6 @@ class Report
     dump_formula_report :A, "New Formulae"
     dump_formula_report :M, "Updated Formulae"
     dump_formula_report :D, "Deleted Formulae"
-    dump_formula_report :R, "Renamed Formulae"
   end
 
   def tapped_formula_for key

Library/Homebrew/test/fixtures/updater_fixture.yaml

@@ -12,7 +12,6 @@ update_git_diff_output_with_formulae_changes: |
   A	Library/Formula/ddrescue.rb
   A	Library/Formula/dict.rb
   A	Library/Formula/lua.rb
-  R094	Library/Formula/shapefile.rb	Library/Formula/shapelib.rb
   M	Library/Formula/xar.rb
   M	Library/Formula/yajl.rb
   M	Library/Homebrew/ARGV+yeast.rb

Library/Homebrew/test/test_updater.rb

@@ -56,7 +56,7 @@ class UpdaterTests < Homebrew::TestCase
       @updater.in_repo_expect("git config core.autocrlf false")
       @updater.in_repo_expect("git pull -q origin refs/heads/master:refs/remotes/origin/master")
       @updater.in_repo_expect("git rev-parse -q --verify HEAD", "3456cdef")
-      @updater.in_repo_expect("git diff-tree -r --name-status -M85% 1234abcd 3456cdef", diff_output)
+      @updater.in_repo_expect("git diff-tree -r --name-status --diff-filter=AMD 1234abcd 3456cdef", diff_output)
       @updater.pull!
       @report.update(@updater.report)
     end
@@ -73,7 +73,7 @@ class UpdaterTests < Homebrew::TestCase
     assert_predicate @updater, :expectations_met?
     assert_empty @report.select_formula(:M)
     assert_empty @report.select_formula(:A)
-    assert_empty @report.select_formula(:R)
+    assert_empty @report.select_formula(:D)
   end
 
   def test_update_homebrew_with_formulae_changes
@@ -81,7 +81,6 @@ class UpdaterTests < Homebrew::TestCase
     assert_predicate @updater, :expectations_met?
     assert_equal %w{ xar yajl }, @report.select_formula(:M)
     assert_equal %w{ antiword bash-completion ddrescue dict lua }, @report.select_formula(:A)
-    assert_equal %w{ shapelib }, @report.select_formula(:R)
   end
 
   def test_update_homebrew_with_tapped_formula_changes