[ruby/zlib] gemspec: Remove unused files

Remove the list of executables.

https://github.com/ruby/zlib/commit/6a70725b8e

ext/zlib/zlib.gemspec

@@ -22,9 +22,9 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://github.com/ruby/zlib"
   spec.licenses       = ["Ruby", "BSD-2-Clause"]
 
-  spec.files         = [".gitignore", ".travis.yml", "Gemfile", "LICENSE.txt", "README.md", "Rakefile", "bin/console", "bin/setup", "ext/zlib/extconf.rb", "ext/zlib/zlib.c", "zlib.gemspec"]
+  spec.files         = ["LICENSE.txt", "README.md", "ext/zlib/extconf.rb", "ext/zlib/zlib.c", "zlib.gemspec"]
   spec.bindir        = "exe"
-  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.executables   = []
   spec.require_paths = ["lib"]
   spec.extensions    = "ext/zlib/extconf.rb"
   spec.required_ruby_version = ">= 2.3.0"