RUBY-3095 remove readConcernLevel special case (#2609)

Co-authored-by: Oleg Pudeyev <[email protected]>

Author: p-mongo

lib/mongo/uri/options_mapper.rb

@@ -102,10 +102,6 @@ def smc_to_ruby(opts)
             uri_options
           end
 
-          if key == 'readConcernLevel'
-            value = value.to_sym
-          end
-
           value = apply_transform(key, value, strategy[:type])
           # Sometimes the value here would be nil, for example if we are processing
           # read preference tags or auth mechanism properties and all of the