Use Heading component on Credits and Subscribe page

Adapt the entering animation as well, SiteTitle was fading

src/style/pages/_credits.scss

@@ -1,28 +1,5 @@
 // Credits Page
 .credits {
-    // Intro Section
-    &__heading {
-        margin: 56px 0 72px;
-        color: $color-tertiary;
-        text-align: center;
-
-        @include bp (md) {
-            margin: 160px 0;
-        }
-
-        // Text
-        p {
-            max-width: 320px;
-            margin: 50px auto 0;
-            font-weight: 200;
-
-            @include bp (sm) {
-                margin: 72px auto 0;
-                max-width: 450px;
-            }
-        }
-    }
-
     // List
     &__list {
         padding-bottom: 96px;