docs: Update security e-mail address correctly.

I updated the text but missed the mailto.  I just removed the mailto
since it's not needed for the address to render properly.

README.rst

@@ -3,7 +3,7 @@
 This repository is deprecated and in maintainence-only operation while we work on a replacement, please see `this announcement <https://discuss.openedx.org/t/deprecation-removal-ecommerce-service-depr-22/6839>`__ for more information.
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-Although we have stopped integrating new contributions, we always appreciate security disclosures and patches sent to `[email protected] <mailto:[email protected]>`__
+Although we have stopped integrating new contributions, we always appreciate security disclosures and patches sent to [email protected]
 
 edX E-Commerce Service  |CI|_ |Codecov|_
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