Revert "Disable deprecation warning by the default [Feature #16345]"

* This reverts commit 56613b1.
* Instead we should just enable deprecation warnings in MSpec.

core/data/constants_spec.rb

@@ -1,15 +1,13 @@
 require_relative '../../spec_helper'
 
-ruby_version_is ""..."3.0" do
-  describe "Data" do
-    it "is a subclass of Object" do
-      suppress_warning do
-        Data.superclass.should == Object
-      end
+describe "Data" do
+  it "is a subclass of Object" do
+    suppress_warning do
+      Data.superclass.should == Object
     end
+  end
 
-    it "is deprecated" do
-      -> { Data }.should complain(/constant ::Data is deprecated/)
-    end
+  it "is deprecated" do
+    -> { Data }.should complain(/constant ::Data is deprecated/)
   end
 end

core/env/index_spec.rb

@@ -1,14 +1,12 @@
 require_relative '../../spec_helper'
 require_relative 'shared/key'
 
-ruby_version_is ""..."3.0" do
-  describe "ENV.index" do
-    it_behaves_like :env_key, :index
+describe "ENV.index" do
+  it_behaves_like :env_key, :index
 
-    it "warns about deprecation" do
-      -> do
-        ENV.index("foo")
-      end.should complain(/warning: ENV.index is deprecated; use ENV.key/)
-    end
+  it "warns about deprecation" do
+    -> do
+      ENV.index("foo")
+    end.should complain(/warning: ENV.index is deprecated; use ENV.key/)
   end
 end

core/integer/constants_spec.rb

@@ -1,27 +1,25 @@
 require_relative '../../spec_helper'
 
-ruby_version_is ""..."3.0" do
-  describe "Fixnum" do
-    it "is unified into Integer" do
-      suppress_warning do
-        Fixnum.should equal(Integer)
-      end
+describe "Fixnum" do
+  it "is unified into Integer" do
+    suppress_warning do
+      Fixnum.should equal(Integer)
     end
+  end
 
-    it "is deprecated" do
-      -> { Fixnum }.should complain(/constant ::Fixnum is deprecated/)
-    end
+  it "is deprecated" do
+    -> { Fixnum }.should complain(/constant ::Fixnum is deprecated/)
   end
+end
 
-  describe "Bignum" do
-    it "is unified into Integer" do
-      suppress_warning do
-        Bignum.should equal(Integer)
-      end
+describe "Bignum" do
+  it "is unified into Integer" do
+    suppress_warning do
+      Bignum.should equal(Integer)
     end
+  end
 
-    it "is deprecated" do
-      -> { Bignum }.should complain(/constant ::Bignum is deprecated/)
-    end
+  it "is deprecated" do
+    -> { Bignum }.should complain(/constant ::Bignum is deprecated/)
   end
 end

core/kernel/match_spec.rb

@@ -14,7 +14,7 @@
     end
   end
 
-  ruby_version_is "2.6"..."3.0" do
+  ruby_version_is "2.6" do
     it "is deprecated" do
       -> do
         Object.new =~ /regexp/

core/module/deprecate_constant_spec.rb

@@ -10,16 +10,6 @@
     @module.private_constant :PRIVATE
     @module.deprecate_constant :PRIVATE
     @pattern = /deprecated/
-    if Warning.respond_to?(:[])
-      @deprecated = Warning[:deprecated]
-      Warning[:deprecated] = true
-    end
-  end
-
-  after :each do
-    if Warning.respond_to?(:[])
-      Warning[:deprecated] = @deprecated
-    end
   end
 
   describe "when accessing the deprecated module" do

language/predefined_spec.rb

@@ -654,7 +654,7 @@ def foo
     -> { $, = Object.new }.should raise_error(TypeError)
   end
 
-  ruby_version_is "2.7"..."3.0" do
+  ruby_version_is "2.7" do
     it "warns if assigned non-nil" do
       -> { $, = "_" }.should complain(/warning: `\$,' is deprecated/)
     end
@@ -693,7 +693,7 @@ def foo
     $; = nil
   end
 
-  ruby_version_is "2.7"..."3.0" do
+  ruby_version_is "2.7" do
     it "warns if assigned non-nil" do
       -> { $; = "_" }.should complain(/warning: `\$;' is deprecated/)
     end

library/net/http/HTTPServerException_spec.rb

@@ -13,7 +13,7 @@
   end
 end
 
-ruby_version_is "2.6"..."3.0" do
+ruby_version_is "2.6" do
   describe "Net::HTTPServerException" do
     it "is a subclass of Net::ProtoServerError and is warned as deprecated" do
       -> { Net::HTTPServerException.should < Net::ProtoServerError }.should complain(/warning: constant Net::HTTPServerException is deprecated/)