Undeprecate Gem::Version#<=> against strings

This pattern is extremely common across the ecosystem, I don't think
it's reasonable to deprecate it.

I understand the performance argument, but perhaps the dependency
resolution algorithm can use another method that is private API
and only works with two `Version` instance.

Author: byroot

lib/rubygems/version.rb

@@ -344,9 +344,6 @@ def approximate_recommendation
 
   def <=>(other)
     if String === other
-      unless Gem::Deprecate.skip
-        warn "comparing version objects with strings is deprecated and will be removed", uplevel: 1
-      end
       return unless self.class.correct?(other)
       return self <=> self.class.new(other)
     end

test/rubygems/test_gem_version.rb

@@ -160,11 +160,7 @@ def test_spaceship
       [-1, "1.9.3.1"],
       [nil, "whatever"],
     ].each do |cmp, string_ver|
-      actual_stdout, actual_stderr = capture_output do
-        assert_equal(cmp, v("1.9.3") <=> string_ver)
-      end
-      assert_empty actual_stdout
-      assert_match(/comparing version objects with strings is deprecated and will be removed/, actual_stderr)
+      assert_equal(cmp, v("1.9.3") <=> string_ver)
     end
   end