[ruby/logger] gemspec: Drop unused "executables" configuration

This gem exposes 0 executables.

https://github.com/ruby/logger/commit/fbd9315393

lib/logger/logger.gemspec

@@ -16,8 +16,6 @@ Gem::Specification.new do |spec|
   spec.licenses      = ["Ruby", "BSD-2-Clause"]
 
   spec.files         = Dir.glob("lib/**/*.rb") + ["logger.gemspec"]
-  spec.bindir        = "exe"
-  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
   spec.required_ruby_version = ">= 2.3.0"