minor #6933 Misplaced paragraph about placeholders in routing.rst (antoin-m)

This PR was merged into the 2.7 branch.

Discussion
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Misplaced paragraph about placeholders in routing.rst

It looks that this paragraph was only a misplaced duplicate of [this block](https://github.com/symfony/symfony-docs/blame/c72dde0a8e90ec9fb90b31e472b2c1e0fac35a37/routing.rst#L259-L262)

As you can see on [this commit](6e48cee?short_path=51326f5#diff-3b3b9409bff44f4b31ba1f933dbf0001L338) the paragraph was originally added to the [Giving {placeholders} a Default Value](https://github.com/symfony/symfony-docs/blob/2.7/routing.rst#giving-placeholders-a-default-value) part.

Commits
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6dcf85a Update routing.rst

Author: xabbuh

routing.rst

@@ -591,10 +591,6 @@ sees our annotation routes:
 For more details on loading routes, including how to prefix the paths of loaded routes,
 see :doc:`/routing/external_resources`.
 
-The path will *not*, however, match simply ``/blog``. That's because,
-by default, all placeholders are required. This can be changed by adding
-a placeholder value to the ``defaults`` array.
-
 .. index::
    single: Routing; Generating URLs