Improve wording of the drawback

During the FCP, people noticed that the wording of the drawback
probably fit better with an earlier draft of this RFC.  Let's
incorporate that feedback before merging.

(Thanks to Waffle for raising this point.)

Author: traviscross

text/0000-unsafe-extern-blocks.md

@@ -95,8 +95,7 @@ Extern statics can be either immutable or mutable just like statics outside of e
 # Drawbacks
 [drawbacks]: #drawbacks
 
-* It is very unfortunate to have to essentially reverse the status quo.
-  * Hopefully, allowing people to safely call some foreign functions will make up for the churn caused by this change.
+This change will induce some churn. Hopefully, allowing people to safely call some foreign functions will make up for that.
 
 # Rationale and alternatives
 [rationale-and-alternatives]: #rationale-and-alternatives