[ruby/ostruct] Drop unused directives from gemspec (https://github.com/ruby/ostruct/pull/39)

This gem exposes no executables.

https://github.com/ruby/ostruct/commit/a1242f7ebe

lib/ostruct/ostruct.gemspec

@@ -20,8 +20,6 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = ">= 2.5.0"
 
   spec.files         = [".gitignore", "Gemfile", "LICENSE.txt", "README.md", "Rakefile", "bin/console", "bin/setup", "lib/ostruct.rb", "ostruct.gemspec"]
-  spec.bindir        = "exe"
-  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
   spec.add_development_dependency "bundler"