WebUI: Remove --cr-primary-text mixin

The mixin was only being used on the Extensions page; all other uses
just use the --cr-primary-text-color variable. The line-height of 154%
is already set on the body element of the Extensions page [1] so it
does not need to be added.

https://imgur.com/a/XsOb3jC

[1] https://cs.chromium.org/chromium/src/chrome/browser/resources/extensions/extensions.html?type=cs&q=extensions.html&sq=package:chromium&g=0&l=52

Bug: 973674
Change-Id: I7c4f5d22ae6d1a77227247cc5abf654246815f18
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1703093Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#678039}

chrome/browser/resources/extensions/item.html

@@ -91,7 +91,7 @@
       }
 
       #name-and-version {
-        @apply --cr-primary-text;
+        color: var(--cr-primary-text-color);
         margin-bottom: 4px;
       }
 

chrome/browser/resources/extensions/keyboard_shortcuts.html

@@ -17,10 +17,10 @@
       }
 
       .shortcut-card {
-        @apply --cr-primary-text;
         @apply --cr-card-elevation;
         background-color: var(--cr-card-background-color);
         border-radius: var(--cr-card-border-radius);
+        color: var(--cr-primary-text-color);
         margin: 0 auto 16px auto;
         padding-bottom: 8px;
         width: var(--cr-toolbar-field-width);

ui/webui/resources/cr_elements/shared_vars_css.html

@@ -154,11 +154,6 @@
       margin-inline-start: var(--cr-icon-button-margin-start);
     }
 
-    --cr-primary-text: {
-      color: var(--cr-primary-text-color);
-      line-height: 154%;  /* 20px. */
-    }
-
     --cr-secondary-text: {
       color: var(--cr-secondary-text-color);
       font-weight: 400;