Remove all-contributors badge link until its updated (#3928)

# Description

The all-contributors badge link was still active at the top of our
Readme file. Not all contirbutors have been added so waiting until that
is complete before adding the badge back.

# Changed Behaviour

N/A

# Fixes

N/A

## Type of change

Choose which options apply, and delete the ones which do not apply.

- Update to human readable text: Documentation/error messages/comments

Author: sophie-bui

README.rst

@@ -1,6 +1,6 @@
 Parsl - Parallel Scripting Library
 ==================================
-|licence| |docs| |All Contributors| |NSF-1550588| |NSF-1550476| |NSF-1550562| |NSF-1550528| |NumFOCUS| |CZI-EOSS| 
+|licence| |docs| |NSF-1550588| |NSF-1550476| |NSF-1550562| |NSF-1550528| |NumFOCUS| |CZI-EOSS| 
 
 Parsl extends parallelism in Python beyond a single computer.