Revert "CSV.open: detect BOM by default"

This reverts commit b706d91.

lib/csv.rb

@@ -1581,14 +1581,7 @@ def generate_lines(rows, **options)
     def open(filename, mode="r", **options)
       # wrap a File opened with the remaining +args+ with no newline
       # decorator
-      file_opts = {}
-      have_encoding_options = (options.key?(:encoding) or
-                               options.key?(:external_encoding) or
-                               mode.include?(":"))
-      if not have_encoding_options and Encoding.default_external == Encoding::UTF_8
-        file_opts[:encoding] = "bom|utf-8"
-      end
-      file_opts.merge!(options)
+      file_opts = options.dup
       unless file_opts.key?(:newline)
         file_opts[:universal_newline] ||= false
       end

test/csv/interface/test_read.rb

@@ -215,16 +215,6 @@ def test_open_with_newline
     end
   end
 
-  def test_open_with_bom
-    csv_data = @input.read
-    bom = "\ufeff" # U+FEFF ZERO WIDTH NO-BREAK SPACE
-    File.binwrite(@input.path, "#{bom}#{csv_data}")
-    @input.rewind
-    CSV.open(@input.path, col_sep: "\t") do |csv|
-      assert_equal(@rows, csv.to_a)
-    end
-  end
-
   def test_parse
     assert_equal(@rows,
                  CSV.parse(@data, col_sep: "\t", row_sep: "\r\n"))