Make the create catalog dialog freely resizable

Fixes #1787523 [generate catalogue doesnt fit in 720](https://bugs.launchpad.net/calibre/+bug/1787523)

src/calibre/gui2/dialogs/catalog.ui

@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>674</width>
-    <height>660</height>
+    <height>645</height>
    </rect>
   </property>
   <property name="windowTitle">
@@ -39,12 +39,6 @@
        <verstretch>0</verstretch>
       </sizepolicy>
      </property>
-     <property name="minimumSize">
-      <size>
-       <width>650</width>
-       <height>575</height>
-      </size>
-     </property>
      <property name="currentIndex">
       <number>0</number>
      </property>