[ruby/net-protocol] Drop unused gemspec directives

This gem exposes no executables.

https://github.com/ruby/net-protocol/commit/3c4def2a64

lib/net/net-protocol.gemspec

@@ -27,8 +27,6 @@ Gem::Specification.new do |spec|
   spec.files         = Dir.chdir(File.expand_path('..', __FILE__)) do
     `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 "timeout"