contributor-guide: remove obsolete pkg-config guidelines

They were coming from obsolete notes from the times
when people directly created or modified .pc files
from their recipes. Nobody should be doing that
any more and keep this can be confusing.

(From yocto-docs rev: 6b3bbf9507ac7014e95926d69383b585c5e19371)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/contributor-guide/recipe-style-guide.rst

@@ -255,8 +255,3 @@ Tips and Guidelines for Writing Recipes
 -  Use :term:`BBCLASSEXTEND` instead of creating separate recipes such as ``-native``
    and ``-nativesdk`` ones, whenever possible. This avoids having to maintain multiple
    recipe files at the same time.
-
--  Avoid manually mangling ``pkg-config`` ``.pc`` files.
-   Recipes using ``pkg-config`` should use variables to ensure they are correctly
-   relocatable and not need manual path correction in the recipe.
-