Fix install_name massaging for keg-only brews

Fixes Homebrew/homebrew#6065.

My pre-emptive fix that avoided calling Pathname.ensure_writable because I was not convinced it worked broke this function due to incorrect logic.

The lesson is, don’t write pre-emptive fixes. Wait until you've seen the bug first. All code has bugs in, so write less. I'm an idiot sometimes.

Library/Homebrew/keg_fix_install_names.rb

@@ -2,9 +2,6 @@ class Keg
   def fix_install_names
     dylibs.each do |dylib|
       bad_install_names_for dylib do |id, bad_names|
-        # avoid the chmod change if unecessary—I'm not convinced it reverses right
-        next if bad_names.empty? and id.to_s == dylib.to_s
-
         dylib.ensure_writable do
           system "install_name_tool", "-id", id, dylib
           bad_names.each do |bad_name|