[ruby/benchmark] gemspec: Explicitly have 0 executables

This gem exposes no executables.

https://github.com/ruby/benchmark/commit/ff1ef7ae06

lib/benchmark/benchmark.gemspec

@@ -24,6 +24,6 @@ Gem::Specification.new do |spec|
     `git ls-files -z 2>/dev/null`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
   end
   spec.bindir        = "exe"
-  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.executables   = []
   spec.require_paths = ["lib"]
 end