[ruby/net-http] gemspec: Drop unused directive "executables"

This gem exposes no executable files.

https://github.com/ruby/net-http/commit/3b3743f6ce

lib/net/http/net-http.gemspec

@@ -28,7 +28,6 @@ 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.require_paths = ["lib"]
 
   spec.add_dependency "net-protocol"