Revert "Paste primary selection into forms on Shift-Insert."

This reverts commit 68a0428a09.

Even if this works fine for me, various people reported segfault issues when
using Shift-Insert, so I'm reverting this for now until I find a proper
solution.

See #491.

qutebrowser/browser/webview.py

@@ -23,9 +23,8 @@ import sys
 import itertools
 import functools
 
-from PyQt5.QtCore import pyqtSignal, pyqtSlot, Qt, QTimer, QUrl, QMimeData
+from PyQt5.QtCore import pyqtSignal, pyqtSlot, Qt, QTimer, QUrl
 from PyQt5.QtWidgets import QApplication, QStyleFactory
-from PyQt5.QtGui import QClipboard
 from PyQt5.QtWebKit import QWebSettings
 from PyQt5.QtWebKitWidgets import QWebView, QWebPage
 
@@ -302,30 +301,6 @@ class WebView(QWebView):
             self.open_target = usertypes.ClickTarget.normal
             log.mouse.debug("Normal click, setting normal target")
 
-    def _paste_primary_selection(self):
-        """Paste the primary selection into the webview.
-
-        This is triggered by keyPressEvent when the user presses Shift-Insert.
-
-        Since QWebView has no way to paste the primary selection instead of the
-        clipboard we get the clipboard data, save it, copy primary selection to
-        clipboard, then paste and restore clipboard data.
-        """
-        clipboard = QApplication.clipboard()
-        selection_data = clipboard.mimeData(QClipboard.Selection)
-        # As soon as we set the new data, the older QMimeData object will be
-        # invalidated which would lead to segfaults - this means we have to
-        # construct a copy of the data by hand.
-        clipboard_data = clipboard.mimeData()
-        new_clipboard_data = QMimeData()
-        for mimetype in clipboard_data.formats():
-            data = clipboard_data.data(mimetype)
-            new_clipboard_data.setData(mimetype, data)
-
-        clipboard.setMimeData(selection_data)
-        self.triggerPageAction(QWebPage.Paste)
-        clipboard.setMimeData(new_clipboard_data)
-
     def shutdown(self):
         """Shut down the webview."""
         # We disable javascript because that prevents some segfaults when
@@ -559,12 +534,3 @@ class WebView(QWebView):
         # We want to make sure we check the focus element after the WebView is
         # updated completely.
         QTimer.singleShot(0, self.mouserelease_insertmode)
-
-    def keyPressEvent(self, e):
-        """Override keyPressEvent to paste primary selection on Shift + Ins."""
-        if e.key() == Qt.Key_Insert and e.modifiers() == Qt.ShiftModifier:
-            if QApplication.clipboard().supportsSelection():
-                e.accept()
-                self._paste_primary_selection()
-                return
-        super().keyPressEvent(e)