(CAT-2155) Remove parser swap to JSON::Pure

`JSON::Pure` no longer exists within the `json` gem as of `2.8.0` and as such this swap has to be removed.

lib/pdk/validate/metadata/metadata_syntax_validator.rb

@@ -22,15 +22,6 @@ def invoke(report)
           JSON.parser = JSON::Ext::Parser if defined?(JSON::Ext::Parser)
         end
 
-        def before_validation
-          # The pure ruby JSON parser gives much nicer parse error messages than
-          # the C extension at the cost of slightly slower parsing. We require it
-          # here and restore the C extension at the end of the method (if it was
-          # being used).
-          require 'json/pure'
-          JSON.parser = JSON::Pure::Parser
-        end
-
         def validate_target(report, target)
           unless PDK::Util::Filesystem.readable?(target)
             report.add_event(

pdk.gemspec

@@ -47,7 +47,6 @@ Gem::Specification.new do |spec|
   # Other deps
   spec.add_runtime_dependency 'deep_merge', '~> 1.2.2'
   spec.add_runtime_dependency 'diff-lcs', '>= 1.5.0'
-  spec.add_runtime_dependency 'json', '< 2.8.0'
   spec.add_runtime_dependency 'pathspec', '~> 1.1'
   spec.add_runtime_dependency 'puppet_forge', '~> 5.0'