fix(multiple): remove .import.scss and -legacy-index.scss files (#27571)

BREAKING CHANGE:
`@import` of Angular Material and Angular CDK Sass is no longer
supported. Please use `@use` instead.

Author: mmalerba

.stylelintrc.json

@@ -43,12 +43,7 @@
         "filePattern": "\\.scss$"
       }
     ],
-    "material/no-import": [
-      true,
-      {
-        "exclude": "\\.import\\.scss$"
-      }
-    ],
+    "material/no-import": true,
     "material/no-ampersand-beyond-selector-start": [
       true,
       {

src/cdk/a11y/_index.import.scss

@@ -23,7 +23,6 @@ sass_library(
     name = "sass_lib",
     srcs = [
         "_index.scss",
-        "_theming.scss",
         "_token-theming.scss",
     ],
     deps = [
@@ -54,14 +53,14 @@ ng_package(
         ":package_json",
         ":sass_lib",
         "//src/material/core:theming_scss_lib",
-        "//src/material/prebuilt-themes:deeppurple-amber",
-        "//src/material/prebuilt-themes:indigo-pink",
-        "//src/material/prebuilt-themes:pink-bluegrey",
-        "//src/material/prebuilt-themes:purple-green",
         "//src/material/legacy-prebuilt-themes:deeppurple-amber",
         "//src/material/legacy-prebuilt-themes:indigo-pink",
         "//src/material/legacy-prebuilt-themes:pink-bluegrey",
         "//src/material/legacy-prebuilt-themes:purple-green",
+        "//src/material/prebuilt-themes:deeppurple-amber",
+        "//src/material/prebuilt-themes:indigo-pink",
+        "//src/material/prebuilt-themes:pink-bluegrey",
+        "//src/material/prebuilt-themes:purple-green",
     ] + MATERIAL_SCSS_LIBS,
     nested_packages = ["//src/material/schematics:npm_package"],
     tags = ["release-package"],

src/cdk/overlay/_index.import.scss

@@ -46,13 +46,9 @@ ALL_THEMING_FILES = [
     # on the `_all-typography` file.
     "_core.scss",
     "color/_all-color.scss",
-    "color/_all-color.import.scss",
     "density/private/_all-density.scss",
-    "density/private/_all-density.import.scss",
     "theming/_all-theme.scss",
-    "theming/_all-theme.import.scss",
     "typography/_all-typography.scss",
-    "typography/_all-typography.import.scss",
 ]
 
 sass_library(