(css) Drop unused "theme" Sass files

Only the original ng-material theme files are used in the build process
of ng-material (using gulp).

UI/WebServerResources/scss/components/dialog/dialog-theme.scss

@@ -1,11 +0,0 @@
-$dialog-border-radius: 4px !default;
-
-md-dialog.md-THEME_NAME-theme {
-  border-radius: $dialog-border-radius;
-  background-color: '{{background-hue-3}}';
-
-  &.md-content-overflow .md-actions {
-    border-top-color: '{{foreground-4}}';
-  }
-}
-