JP 11: [thread.mutex.requirements.general] Remove outdated sentence.

This sentence directly contradicts several other portions of the
standard, and does not reflect the intended meaning.

Author: zygoloid

source/threads.tex

@@ -888,8 +888,7 @@
 data between execution agents~(\ref{thread.req.lockable}).
 An execution agent \term{owns} a mutex from the time it successfully calls one of the
 lock functions until it calls unlock. Mutexes can be either recursive or non-recursive, and can
-grant simultaneous ownership to one or many execution agents. The mutex types supplied by the standard
-library provide exclusive ownership semantics: only one thread may own the mutex at a time. Both
+grant simultaneous ownership to one or many execution agents. Both
 recursive and non-recursive mutexes are supplied.
 
 \rSec3[thread.mutex.requirements.mutex]{Mutex types}