Remove duplicate tests

tests/wpt/mozilla/meta/MANIFEST.json

@@ -23824,7 +23824,7 @@
    "support"
   ],
   "css/test_font_family_parsing.html": [
-   "e0df1ad62a5c72e841806c0debd64a36d2898abe",
+   "fb9155875cb9cee7eba6e7a9be311ef02c82a869",
    "testharness"
   ],
   "css/test_variable_legal_values.html": [
@@ -23836,7 +23836,7 @@
    "testharness"
   ],
   "css/test_variable_serialization_specified.html": [
-   "70137258ef07c0983e0927aacbab5ed87b037b54",
+   "b403085f651089d08d6a22731b1a255c357b20c7",
    "testharness"
   ],
   "css/text_align_complex_a.html": [

tests/wpt/mozilla/tests/css/test_font_family_parsing.html

@@ -81,7 +81,6 @@ var testFontFamilyLists = [
   { namelist: "\\@font-face", single: true },
   { namelist: "\\@font-face\\;", single: true },
   { namelist: "\\031 \\036 px", single: true },
-  { namelist: "\\031 \\036 px", single: true },
   { namelist: "\\1f4a9", single: true },
   { namelist: "\\01f4a9", single: true },
   { namelist: "\\0001f4a9", single: true },

tests/wpt/mozilla/tests/css/test_variable_serialization_specified.html

@@ -18,7 +18,6 @@ so an implementation could fail this test but still be conforming.
 <script>
 // Values that should be serialized back to the same string.
 var values_with_unchanged_specified_value_serialization = [
-  "var(--a)",
   "var(--a)",
   "var(--a) ",
   "var( --a ) ",
@@ -27,7 +26,6 @@ var values_with_unchanged_specified_value_serialization = [
   "1px var(--a)",
   "var(--a) 1px",
   "something 3px url(whereever) calc(var(--a) + 1px)",
-  "var(--a)",
   "var(--a)var(--b)",
   "var(--a, var(--b, var(--c, black)))",
   "var(--a) <!--",