Use `rb_warn_deprecated` for `File.exists?` and `Dir.exists?`

dir.c

@@ -3498,7 +3498,7 @@ rb_file_directory_p(void)
 static VALUE
 rb_dir_exists_p(VALUE obj, VALUE fname)
 {
-    rb_warning("Dir.exists? is a deprecated name, use Dir.exist? instead");
+    rb_warn_deprecated("", "Dir.exist?");
     return rb_file_directory_p(obj, fname);
 }
 

file.c

@@ -1782,16 +1782,16 @@ rb_file_exist_p(VALUE obj, VALUE fname)
 static VALUE
 rb_file_exists_p(VALUE obj, VALUE fname)
 {
-    const char *s = "FileTest#";
+    const char *s = "FileTest#exist?";
     if (obj == rb_mFileTest) {
-	s = "FileTest.";
+	s = "FileTest.exist?";
     }
     else if (obj == rb_cFile ||
 	     (RB_TYPE_P(obj, T_CLASS) &&
 	      RTEST(rb_class_inherited_p(obj, rb_cFile)))) {
-	s = "File.";
+	s = "File.exist?";
     }
-    rb_warning("%sexists? is a deprecated name, use %sexist? instead", s, s);
+    rb_warn_deprecated("", s);
     return rb_file_exist_p(obj, fname);
 }
 

spec/ruby/core/dir/exists_spec.rb

@@ -1,15 +0,0 @@
-require_relative '../../spec_helper'
-require_relative 'fixtures/common'
-require_relative 'shared/exist'
-
-describe "Dir.exists?" do
-  before :all do
-    DirSpecs.create_mock_dirs
-  end
-
-  after :all do
-    DirSpecs.delete_mock_dirs
-  end
-
-  it_behaves_like :dir_exist, :exists?
-end

spec/ruby/core/file/exists_spec.rb

@@ -1,6 +0,0 @@
-require_relative '../../spec_helper'
-require_relative '../../shared/file/exist'
-
-describe "File.exists?" do
-  it_behaves_like :file_exist, :exists?, File
-end

spec/ruby/core/filetest/exists_spec.rb

@@ -1,6 +0,0 @@
-require_relative '../../spec_helper'
-require_relative '../../shared/file/exist'
-
-describe "FileTest.exists?" do
-  it_behaves_like :file_exist, :exists?, FileTest
-end