Stop overriding specs during double-checks

This fixes my test-case reproduction of #6072. I’m pretty sure it’s
because the double-check was overriding the locally installed index
specs with specs fetched from the RubyGems API, causing Bundler to
conclude that the gems aren’t installed, even though they are.

lib/bundler/definition.rb

@@ -294,7 +294,7 @@ def double_check_for_index(idx, dependency_names)
         end
 
         sources.all_sources.each do |source|
-          source.double_check_for(unmet_dependency_names, :override_dupes)
+          source.double_check_for(unmet_dependency_names)
         end
 
         break if idxcount == idx.size

lib/bundler/source/rubygems.rb

@@ -258,10 +258,8 @@ def fetchers
         end
       end
 
-      def double_check_for(unmet_dependency_names, override_dupes = false, index = specs)
+      def double_check_for(unmet_dependency_names)
         return unless @allow_remote
-        raise ArgumentError, "missing index" unless index
-
         return unless api_fetchers.any?
 
         unmet_dependency_names = unmet_dependency_names.call
@@ -276,7 +274,7 @@ def double_check_for(unmet_dependency_names, override_dupes = false, index = spe
 
         Bundler.ui.debug "Double checking for #{unmet_dependency_names || "all specs (due to the size of the request)"} in #{self}"
 
-        fetch_names(api_fetchers, unmet_dependency_names, index, override_dupes)
+        fetch_names(api_fetchers, unmet_dependency_names, specs, false)
       end
 
       def dependency_names_to_double_check