Deprecate taint/trust and related methods, and make the methods no-ops

This removes the related tests, and puts the related specs behind
version guards.  This affects all code in lib, including some
libraries that may want to support older versions of Ruby.

spec/ruby/core/string/modulo_spec.rb

@@ -297,24 +297,26 @@ describe "String#%" do
     end
   end
 
-  it "always taints the result when the format string is tainted" do
-    universal = mock('0')
-    def universal.to_int() 0 end
-    def universal.to_str() "0" end
-    def universal.to_f() 0.0 end
+  ruby_version_is ''...'2.7' do
+    it "always taints the result when the format string is tainted" do
+      universal = mock('0')
+      def universal.to_int() 0 end
+      def universal.to_str() "0" end
+      def universal.to_f() 0.0 end
 
-    [
-      "", "foo",
-      "%b", "%B", "%c", "%d", "%e", "%E",
-      "%f", "%g", "%G", "%i", "%o", "%p",
-      "%s", "%u", "%x", "%X"
-    ].each do |format|
-      subcls_format = StringSpecs::MyString.new(format)
-      subcls_format.taint
-      format.taint
+      [
+        "", "foo",
+        "%b", "%B", "%c", "%d", "%e", "%E",
+        "%f", "%g", "%G", "%i", "%o", "%p",
+        "%s", "%u", "%x", "%X"
+      ].each do |format|
+        subcls_format = StringSpecs::MyString.new(format)
+        subcls_format.taint
+        format.taint
 
-      (format % universal).tainted?.should == true
-      (subcls_format % universal).tainted?.should == true
+        (format % universal).tainted?.should == true
+        (subcls_format % universal).tainted?.should == true
+      end
     end
   end
 
@@ -571,16 +573,18 @@ describe "String#%" do
     # ("%p" % obj).should == "obj"
   end
 
-  it "taints result for %p when argument.inspect is tainted" do
-    obj = mock('x')
-    def obj.inspect() "x".taint end
+  ruby_version_is ''...'2.7' do
+    it "taints result for %p when argument.inspect is tainted" do
+      obj = mock('x')
+      def obj.inspect() "x".taint end
 
-    ("%p" % obj).tainted?.should == true
+      ("%p" % obj).tainted?.should == true
 
-    obj = mock('x'); obj.taint
-    def obj.inspect() "x" end
+      obj = mock('x'); obj.taint
+      def obj.inspect() "x" end
 
-    ("%p" % obj).tainted?.should == false
+      ("%p" % obj).tainted?.should == false
+    end
   end
 
   it "supports string formats using %s" do
@@ -611,9 +615,11 @@ describe "String#%" do
     # ("%s" % obj).should == "obj"
   end
 
-  it "taints result for %s when argument is tainted" do
-    ("%s" % "x".taint).tainted?.should == true
-    ("%s" % mock('x').taint).tainted?.should == true
+  ruby_version_is ''...'2.7' do
+    it "taints result for %s when argument is tainted" do
+      ("%s" % "x".taint).tainted?.should == true
+      ("%s" % mock('x').taint).tainted?.should == true
+    end
   end
 
   # MRI crashes on this one.
@@ -776,8 +782,10 @@ describe "String#%" do
       (format % "0xA").should == (format % 0xA)
     end
 
-    it "doesn't taint the result for #{format} when argument is tainted" do
-      (format % "5".taint).tainted?.should == false
+    ruby_version_is ''...'2.7' do
+      it "doesn't taint the result for #{format} when argument is tainted" do
+        (format % "5".taint).tainted?.should == false
+      end
     end
   end