reverted:
--- b/core/lib/Drupal/Core/Extension/ThemeHandler.php
+++ a/core/lib/Drupal/Core/Extension/ThemeHandler.php
@@ -169,11 +169,6 @@
 
     $this->clearCssCache();
 
-    // Remove configuration.
-    foreach ($theme_list as $key) {
-      \Drupal::service('config.manager')->uninstall('theme', $key);
-    }
-
     $theme_config = $this->configFactory->get('system.theme');
     $disabled_themes = $this->configFactory->get('system.theme.disabled');
     foreach ($theme_list as $key) {
only in patch2:
unchanged:
--- a/core/modules/breakpoint/lib/Drupal/breakpoint/Tests/BreakpointThemeTest.php
+++ b/core/modules/breakpoint/lib/Drupal/breakpoint/Tests/BreakpointThemeTest.php
@@ -51,10 +51,6 @@ public function testThemeBreakpoints() {
 
     // Verify we can load this breakpoint defined by the theme.
     $this->verifyBreakpointGroup($breakpoint_group_obj);
-
-    // Disable the test theme and verify the breakpoint group is deleted.
-    theme_disable(array('breakpoint_test_theme'));
-    $this->assertFalse(entity_load('breakpoint_group', $breakpoint_group_obj->id()), 'breakpoint_group_load: Loading a deleted breakpoint group returns false.', 'Breakpoint API');
   }
 
   /**
@@ -79,10 +75,6 @@ public function testThemeBreakpointGroup() {
 
     // Verify we can load this breakpoint defined by the theme.
     $this->verifyBreakpointGroup($breakpoint_group_obj);
-
-    // Disable the test theme and verify the breakpoint group is deleted.
-    theme_disable(array('breakpoint_test_theme'));
-    $this->assertFalse(entity_load('breakpoint_group', $breakpoint_group_obj->id()), 'breakpoint_group_load: Loading a deleted breakpoint group returns false.', 'Breakpoint API');
   }
 
 }