Backport PR #11947: Update several extensions readme files to delete old content. (#11951)

Co-authored-by: Jason Grout <jasongrout@users.noreply.github.com>

packages/javascript-extension/README.md

@@ -1,19 +1,15 @@
 # javascript-extension
 
-A JupyterLab extension for running Javascript from a notebook in JupyterLab
+A JupyterLab extension for running Javascript from a notebook in JupyterLab.
 
-## Prerequisites
-
-- JupyterLab ^0.27.0
+This extension is in the official JupyterLab distribution.
 
 ## Usage
 
-To render VDOM output in IPython:
-
 ```python
 from IPython.display import Javascript
 
-Javascript('console.log("hello world");')
+Javascript('alert("hello world");')
 ```
 
 ## Development

packages/json-extension/README.md

@@ -4,9 +4,7 @@ A JupyterLab extension for rendering JSON as a tree
 
 ![demo](http://g.recordit.co/mqve0QPqyM.gif)
 
-## Prerequisites
-
-- JupyterLab ^0.27.0
+This extension is in the official JupyterLab distribution.
 
 ## Usage
 

packages/vdom-extension/README.md

@@ -4,9 +4,7 @@ A JupyterLab extension for rendering VirtualDOM using React
 
 ![demo](http://g.recordit.co/EIwAIBsGBh.gif)
 
-## Prerequisites
-
-- JupyterLab ^0.27.0
+This extension is in the official JupyterLab distribution.
 
 ## Usage
 

packages/vdom/README.md

@@ -1,77 +1,6 @@
-# vdom-extension
+# vdom
 
-A JupyterLab extension for rendering VirtualDOM using React
-
-![demo](http://g.recordit.co/EIwAIBsGBh.gif)
-
-## Prerequisites
-
-- JupyterLab ^0.27.0
-
-## Usage
-
-To render VDOM output in IPython:
-
-```python
-from IPython.display import display
-
-def VDOM(data={}):
-    bundle = {}
-    bundle['application/vdom.v1+json'] = data
-    display(bundle, raw=True)
-
-VDOM({
-    'tagName': 'div',
-    'attributes': {},
-    'children': [{
-        'tagName': 'h1',
-        'attributes': {},
-        'children': 'Our Incredibly Declarative Example',
-        'key': 0
-    }, {
-        'tagName': 'p',
-        'attributes': {},
-        'children': ['Can you believe we wrote this ', {
-            'tagName': 'b',
-            'attributes': {},
-            'children': 'in Python',
-            'key': 1
-        }, '?'],
-        'key': 1
-    }, {
-        'tagName': 'img',
-        'attributes': {
-            'src': 'https://media.giphy.com/media/xUPGcguWZHRC2HyBRS/giphy.gif'
-        },
-        'key': 2
-    }, {
-        'tagName': 'p',
-        'attributes': {},
-        'children': ['What will ', {
-            'tagName': 'b',
-            'attributes': {},
-            'children': 'you',
-            'key': 1
-        }, ' create next?'],
-        'key': 3
-    }]
-})
-```
-
-Using the [vdom Python library](https://github.com/nteract/vdom):
-
-```python
-from vdom import h1, p, img, div, b
-
-div(
-    h1('Our Incredibly Declarative Example'),
-    p('Can you believe we wrote this ', b('in Python'), '?'),
-    img(src="https://media.giphy.com/media/xUPGcguWZHRC2HyBRS/giphy.gif"),
-    p('What will ', b('you'), ' create next?'),
-)
-```
-
-To render a `.vdom` or `.vdom.json` file, simply open it:
+A library for rendering VirtualDOM content using React.
 
 ## Development
 

packages/vega5-extension/README.md

@@ -4,9 +4,7 @@ A JupyterLab extension for rendering [Vega](https://vega.github.io/vega) 5 and [
 
 ![demo](http://g.recordit.co/USoTkuCOfR.gif)
 
-## Prerequisites
-
-- JupyterLab ^0.27.0
+This extension is in the official JupyterLab distribution.
 
 ## Usage