Remove confusing sentence from Mutex docs

The docs were saying something about "statically initializing" the
mutex, and it's not clear what this means. Remove that part to avoid
confusion.

library/std/src/sync/mutex.rs

@@ -10,11 +10,10 @@ use crate::sys_common::mutex as sys;
 /// A mutual exclusion primitive useful for protecting shared data
 ///
 /// This mutex will block threads waiting for the lock to become available. The
-/// mutex can also be statically initialized or created via a [`new`]
-/// constructor. Each mutex has a type parameter which represents the data that
-/// it is protecting. The data can only be accessed through the RAII guards
-/// returned from [`lock`] and [`try_lock`], which guarantees that the data is only
-/// ever accessed when the mutex is locked.
+/// mutex can created via a [`new`] constructor. Each mutex has a type parameter
+/// which represents the data that it is protecting. The data can only be accessed
+/// through the RAII guards returned from [`lock`] and [`try_lock`], which
+/// guarantees that the data is only ever accessed when the mutex is locked.
 ///
 /// # Poisoning
 ///