clean up "master file" CSS comments

Author: shawnbot

src/core/index.scss

@@ -1,18 +1,13 @@
 /*!
- * Primer-core
- * http://primer.github.io
+ * @primer/css/core
+ * http://primer.style/css
  *
  * Released under MIT license. Copyright (c) 2019 GitHub Inc.
  */
 
 // Include .octicon base styles
 @import "@primer/octicons/index.scss";
 
-// Primer master file
-//
-// Imports all Primer files in their intended order for easy mass-inclusion.
-// Should you need specific files, you can easily use separate `@import`s.
-
 // Global requirements
 @import "../support/index.scss";
 

src/marketing/index.scss

@@ -1,15 +1,10 @@
 /*!
- * Primer-marketing
- * http://primer.github.io
+ * @primer/css/marketing
+ * http://primer.style/css
  *
  * Released under MIT license. Copyright (c) 2019 GitHub Inc.
  */
 
-// Primer master file
-//
-// Imports all Primer files in their intended order for easy mass-inclusion.
-// Should you need specific files, you can easily use separate `@import`s.
-
 // Global requirements
 @import "./support/index.scss";
 

src/product/index.scss

@@ -1,15 +1,10 @@
 /*!
- * Primer-product
- * http://primer.github.io
+ * @primer/css/product
+ * http://primer.style/css
  *
  * Released under MIT license. Copyright (c) 2019 GitHub Inc.
  */
 
-// Primer master file
-//
-// Imports all Primer files in their intended order for easy mass-inclusion.
-// Should you need specific files, you can easily use separate `@import`s.
-
 // Global requirements
 @import "../support/index.scss";