background: Remove noise texture

Use the plain background color.

Closes: https://gitlab.gnome.org/GNOME/gnome-shell/issues/2174

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/872

data/gnome-shell-theme.gresource.xml

@@ -18,7 +18,6 @@
     <file alias="icons/message-indicator-symbolic.svg">message-indicator-symbolic.svg</file>
     <file>no-events.svg</file>
     <file>no-notifications.svg</file>
-    <file>noise-texture.png</file>
     <file>pad-osd.css</file>
     <file alias="icons/eye-open-negative-filled-symbolic.svg">eye-open-negative-filled-symbolic.svg</file>
     <file alias="icons/eye-not-looking-symbolic.svg">eye-not-looking-symbolic.svg</file>

data/theme/gnome-shell-sass/widgets/_screen-shield.scss

@@ -55,8 +55,7 @@
 }
 
 #lockDialogGroup {
-  background: lighten(#2e3436, 8%) url(resource:///org/gnome/shell/theme/noise-texture.png);
-  background-repeat: repeat;
+  background-color: lighten(#2e3436, 8%);
 }
 
 #unlockDialogNotifications {