[SkeletonThumbnail][SkeletonPage] Consolidate se23 conditional logic (#…

…10143)

### WHY are these changes introduced?

Fixes #9966
Fixes #9967

### WHAT is this pull request doing?

* Consolidate se23 logic and styles for `SkeletonThumbnail` Component
* Consolidate se23 logic and styles for `SkeletonPage` Component

### How to 🎩
* Compare production and this PR's chromatic storybook to make sure
styles are the same

[Production skeleton
page](https://storybook.polaris.shopify.com/?path=/story/all-components-skeletonpage--with-dynamic-content&globals=polarisSummerEditions2023:true)
[This PR skeleton
page](https://5d559397bae39100201eedc1-zxhtnbvnuu.chromatic.com/?path=/story/all-components-skeletonpage--with-dynamic-content)

[Production skeleton
thumbnail](https://storybook.polaris.shopify.com/?path=/story/all-components-skeletonthumbnail--all&globals=polarisSummerEditions2023:true)
[This PR skeleton
thumbnail](https://5d559397bae39100201eedc1-zxhtnbvnuu.chromatic.com/?path=/story/all-components-skeletonthumbnail--all)

polaris-react/src/components/SkeletonPage/SkeletonPage.scss

@@ -11,13 +11,9 @@ $primary-action-button-width: 6.25rem;
 }
 
 .Title {
-  font-weight: var(--p-font-weight-semibold);
+  font-weight: var(--p-font-weight-bold);
   font-size: var(--p-font-size-300);
   line-height: var(--p-font-line-height-4);
-
-  #{$se23} & {
-    font-weight: var(--p-font-weight-bold);
-  }
 }
 
 .SkeletonTitle {

polaris-react/src/components/SkeletonThumbnail/SkeletonThumbnail.scss

@@ -2,22 +2,14 @@
 
 .SkeletonThumbnail {
   // stylelint-disable -- Polaris component custom properties
-  --pc-skeleton-thumbnail-extra-small-size: 24px;
-  --pc-skeleton-thumbnail-small-size: 40px;
+  --pc-skeleton-thumbnail-extra-small-size: 40px;
+  --pc-skeleton-thumbnail-small-size: 48px;
   --pc-skeleton-thumbnail-medium-size: 60px;
   --pc-skeleton-thumbnail-large-size: 80px;
   // stylelint-enable
   display: flex;
   background-color: var(--p-color-bg-strong);
-  border-radius: var(--p-border-radius-1);
-
-  #{$se23} & {
-    // stylelint-disable -- Polaris component custom properties, se23 temporary styles
-    --pc-skeleton-thumbnail-extra-small-size: 40px;
-    --pc-skeleton-thumbnail-small-size: 48px;
-    // stylelint-enable
-    border-radius: var(--p-border-radius-2);
-  }
+  border-radius: var(--p-border-radius-2);
 
   @media screen and (-ms-high-contrast: active) {
     background-color: grayText;