Update settings for QtWebEngine by default

See #2335

doc/help/settings.asciidoc

@@ -291,18 +291,17 @@ Default: +pass:[false]+
 === backend
 The backend to use to display websites.
 qutebrowser supports two different web rendering engines / backends, QtWebKit and QtWebEngine.
-QtWebKit is based on WebKit (similar to Safari). It was discontinued by the Qt project with Qt 5.6, but picked up as a well maintained fork: https://github.com/annulen/webkit/wiki - qutebrowser only supports the fork.
-QtWebEngine is Qt's official successor to QtWebKit and based on the Chromium project. It's slightly more resource hungry that QtWebKit and has a couple of missing features in qutebrowser, but is generally the preferred choice.
+QtWebKit was discontinued by the Qt project with Qt 5.6, but picked up as a well maintained fork: https://github.com/annulen/webkit/wiki - qutebrowser only supports the fork.
+QtWebEngine is Qt's official successor to QtWebKit. It's slightly more resource hungry that QtWebKit and has a couple of missing features in qutebrowser, but is generally the preferred choice.
 
 Type: <<types,String>>
 
 Valid values:
 
- * +auto+: Automatically select either QtWebEngine or QtWebKit
- * +webkit+: Force QtWebKit
- * +webengine+: Force QtWebEngine
+ * +webengine+: Use QtWebEngine (based on Chromium)
+ * +webkit+: Use QtWebKit (based on WebKit, similar to Safari)
 
-Default: +pass:[auto]+
+Default: +pass:[webengine]+
 
 [[bindings.commands]]
 === bindings.commands

qutebrowser/config/configdata.yml

@@ -105,23 +105,22 @@ backend:
   type:
     name: String
     valid_values:
-      - auto: Automatically select either QtWebEngine or QtWebKit
-      - webkit: Force QtWebKit
-      - webengine: Force QtWebEngine
-  default: auto
+      - webengine: Use QtWebEngine (based on Chromium)
+      - webkit: Use QtWebKit (based on WebKit, similar to Safari)
+  default: webengine
   desc: >-
     The backend to use to display websites.
 
     qutebrowser supports two different web rendering engines / backends,
     QtWebKit and QtWebEngine.
 
-    QtWebKit is based on WebKit (similar to Safari). It was discontinued by the
-    Qt project with Qt 5.6, but picked up as a well maintained fork:
-    https://github.com/annulen/webkit/wiki - qutebrowser only supports the fork.
+    QtWebKit was discontinued by the Qt project with Qt 5.6, but picked up as a
+    well maintained fork: https://github.com/annulen/webkit/wiki - qutebrowser
+    only supports the fork.
 
-    QtWebEngine is Qt's official successor to QtWebKit and based on the Chromium
-    project. It's slightly more resource hungry that QtWebKit and has a couple
-    of missing features in qutebrowser, but is generally the preferred choice.
+    QtWebEngine is Qt's official successor to QtWebKit. It's slightly more
+    resource hungry that QtWebKit and has a couple of missing features in
+    qutebrowser, but is generally the preferred choice.
 
 ## auto_save
 

qutebrowser/config/configinit.py

@@ -74,13 +74,6 @@ def early_init(args):
 
 def get_backend(args):
     """Find out what backend to use based on available libraries."""
-    try:
-        import PyQt5.QtWebKit  # pylint: disable=unused-variable
-    except ImportError:
-        webkit_available = False
-    else:
-        webkit_available = qtutils.is_new_qtwebkit()
-
     str_to_backend = {
         'webkit': usertypes.Backend.QtWebKit,
         'webengine': usertypes.Backend.QtWebEngine,
@@ -88,12 +81,8 @@ def get_backend(args):
 
     if args.backend is not None:
         return str_to_backend[args.backend]
-    elif config.val.backend != 'auto':
-        return str_to_backend[config.val.backend]
-    elif webkit_available:
-        return usertypes.Backend.QtWebKit
     else:
-        return usertypes.Backend.QtWebEngine
+        return str_to_backend[config.val.backend]
 
 
 def late_init(save_manager):