os/mac: remove CLT header package stuff.

We never care about it and it's not relevant anywhere except 10.14.

Library/Homebrew/extend/os/mac/system_config.rb

@@ -41,10 +41,6 @@ class SystemConfig
       @clt ||= MacOS::CLT.version if MacOS::CLT.installed?
     end
 
-    def clt_headers
-      @clt_headers ||= MacOS::CLT.headers_version if MacOS::CLT.headers_installed?
-    end
-
     def xquartz
       @xquartz ||= "#{MacOS::XQuartz.version} => #{describe_path(MacOS::XQuartz.prefix)}" if MacOS::XQuartz.installed?
     end
@@ -54,7 +50,6 @@ class SystemConfig
       f.puts "macOS: #{MacOS.full_version}-#{kernel}"
       f.puts "CLT: #{clt || "N/A"}"
       f.puts "Xcode: #{xcode || "N/A"}"
-      f.puts "CLT headers: #{clt_headers}" if MacOS::CLT.separate_header_package? && clt_headers
       f.puts "XQuartz: #{xquartz}" if xquartz
     end
   end

Library/Homebrew/os/mac/xcode.rb

@@ -193,9 +193,6 @@ module OS
       EXECUTABLE_PKG_ID = "com.apple.pkg.CLTools_Executables"
       MAVERICKS_NEW_PKG_ID = "com.apple.pkg.CLTools_Base" # obsolete
       PKG_PATH = "/Library/Developer/CommandLineTools"
-      HEADER_PKG_PATH =
-        "/Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_:macos_version.pkg"
-      HEADER_PKG_ID = "com.apple.pkg.macOS_SDK_headers_for_macOS_10.14"
 
       # Returns true even if outdated tools are installed
       def installed?
@@ -210,14 +207,6 @@ module OS
         version >= "8"
       end
 
-      def headers_installed?
-        if !separate_header_package?
-          installed?
-        else
-          headers_version == version
-        end
-      end
-
       def sdk(v = nil)
         @locator ||= CLTSDKLocator.new
 
@@ -302,19 +291,6 @@ module OS
         end
       end
 
-      # Version string of the header package, which is a
-      # separate package as of macOS 10.14.
-      def headers_version
-        if !separate_header_package?
-          version
-        else
-          @header_version ||= MacOS.pkgutil_info(HEADER_PKG_ID)[/version: (.+)$/, 1]
-          return ::Version::NULL unless @header_version
-
-          ::Version.new(@header_version)
-        end
-      end
-
       def detect_version
         version = nil
         [EXECUTABLE_PKG_ID, MAVERICKS_NEW_PKG_ID].each do |id|