Apply suggestions from code review

Co-authored-by: David Tolnay <dtolnay@gmail.com>

Author: poliorcetics

src/libstd/sync/mutex.rs

@@ -108,8 +108,8 @@ use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult};
 /// *guard += 1;
 /// ```
 ///
-/// It is sometimes a good idea (or even necessary) to manually drop the mutex
-/// to unlock it as soon as possible. If you need the resource until the end of
+/// It is sometimes necessary to manually drop the mutex
+/// guard to unlock it as soon as possible. If you need the resource until the end of
 /// the scope, this is not needed.
 ///
 /// ```
@@ -140,16 +140,16 @@ use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult};
 /// // This is the result of some important and long-ish work.
 /// let result = data.iter().fold(0, |acc, x| acc + x * 2);
 /// data.push(result);
-/// // We drop the `data` explicitely because it's not necessary anymore
+/// // We drop the `data` explicitly because it's not necessary anymore
 /// // and the thread still has work to do. This allow other threads to
 /// // start working on the data immediately, without waiting
 /// // for the rest of the unrelated work to be done here.
 /// //
 /// // It's even more important here than in the threads because we `.join` the
-/// // threads after that. If we had not dropped the lock, a thread could be
+/// // threads after that. If we had not dropped the mutex guard, a thread could be
 /// // waiting forever for it, causing a deadlock.
 /// drop(data);
-/// // Here the lock is not assigned to a variable and so, even if the scope
+/// // Here the mutex guard is not assigned to a variable and so, even if the scope
 /// // does not end after this line, the mutex is still released:
 /// // there is no deadlock.
 /// *res_mutex.lock().unwrap() += result;