Have delete-duplicates/sort! take a equality procedure

And change the default, as eq? doesn't always work.

guix-data-service/model/derivation.scm

@@ -1840,7 +1840,8 @@ WHERE derivation_inputs.derivation_id IN ("
                   (length ids-chunk))
                (exec-query conn query)))))
         (chunk! ids 500))
-       <))
+       <
+       =))
 
     (define (derivation-ids->missing-sources ids)
       (define query

guix-data-service/utils.scm

@@ -417,7 +417,7 @@ available.  Return the resource once PROC has returned."
 
   #t)
 
-(define (delete-duplicates/sort! unsorted-lst less)
+(define* (delete-duplicates/sort! unsorted-lst less #:optional (equal? equal?))
   (if (null? unsorted-lst)
       unsorted-lst
       (let ((sorted-lst (sort! unsorted-lst less)))
@@ -428,7 +428,7 @@ available.  Return the resource once PROC has returned."
           (if (null? lst)
               result
               (let ((current-element (car lst)))
-                (if (eq? current-element last-element)
+                (if (equal? current-element last-element)
                     (loop (cdr lst)
                           last-element
                           result)

guix-data-service/web/compare/html.scm

@@ -865,7 +865,7 @@ enough builds to determine a change")))
                 ((names . new-drvs-count)
                  (let ((distinct-packages
                         (length
-                         (delete-duplicates/sort! names string<?))))
+                         (delete-duplicates/sort! names string<? string=?))))
                    `((p
                       ,(simple-format #f "Showing ~A new derivations across ~A packages"
                                       new-drvs-count