Revert https://codereview.chromium.org/1291903002 (protobuf roll).

third_party/protobuf/ruby/google-protobuf.gemspec

-Gem::Specification.new do |s|
-  s.name        = "google-protobuf"
-  s.version     = "3.0.0.alpha.4.0.pre"
-  s.licenses    = ["BSD"]
-  s.summary     = "Protocol Buffers"
-  s.description = "Protocol Buffers are Google's data interchange format."
-  s.homepage    = "https://developers.google.com/protocol-buffers"
-  s.authors     = ["Protobuf Authors"]
-  s.email       = "protobuf@googlegroups.com"
-  s.require_paths = ["lib"]
-  s.files       = `git ls-files -z`.split("\x0").find_all{|f| f =~ /lib\/.+\.rb/}
-  unless RUBY_PLATFORM == "java"
-    s.files     += `git ls-files "*.c" "*.h" extconf.rb Makefile`.split
-    s.extensions= ["ext/google/protobuf_c/extconf.rb"]
-  else
-    s.files     += ["lib/google/protobuf_java.jar"]
-  end
-  s.test_files  = ["tests/basic.rb",
-                  "tests/stress.rb",
-                  "tests/generated_code_test.rb"]
-  s.add_development_dependency "rake-compiler"
-  s.add_development_dependency "test-unit"
-  s.add_development_dependency "rubygems-tasks"
-end