Deprecate the unintentional ability to parse Symbol

spec/ruby/library/date/iso8601_spec.rb

@@ -17,20 +17,11 @@ describe "Date.iso8601" do
     d.should == Date.civil(-4712, 1, 1)
   end
 
-  it "parses a Symbol into a Date object" do
-    d = Date.iso8601(:'2015-10-15')
-    d.should == Date.civil(2015, 10, 15)
-  end
-
   it "parses a StringSubclass into a Date object" do
     d = Date.iso8601(Class.new(String).new("-4712-01-01"))
     d.should == Date.civil(-4712, 1, 1)
   end
 
-  it "raises an ArgumentError when passed a Symbol without a valid Date" do
-    -> { Date.iso8601(:test) }.should raise_error(ArgumentError)
-  end
-
   it "raises a TypeError when passed an Object" do
     -> { Date.iso8601(Object.new) }.should raise_error(TypeError)
   end

spec/ruby/library/date/parse_spec.rb

@@ -67,7 +67,7 @@ describe "Date#parse" do
 
   it "raises a TypeError trying to parse non-String-like object" do
     -> { Date.parse(1) }.should raise_error(TypeError)
-    -> { Date.parse(:invalid) }.should raise_error(TypeError)
+    -> { Date.parse([]) }.should raise_error(TypeError)
   end
 
   it "coerces using to_str" do