Remove confusing comments

Without an explanation (which is not even present in the original
commit message), the remarks about locking the current task being
unnecessary is confusing at best.

The basic understanding of the code actually suggests that locking
the current task is essential for the mutual exclusion in the mapping
and unmapping routines.

Change-Id: Ia83231367bb0e4c987b75a31fdde38501e43c543

src/kern/task.cpp

@@ -445,7 +445,6 @@ Task::sys_map(L4_fpage::Rights rights, Syscall_frame *f, Utcb *utcb)
       // always take lock from task with the lower memory address first
       Lock_guard_2<Lock> guard;
 
-      // FIXME: avoid locking the current task, it is not needed
       if (!guard.check_and_lock(&existence_lock, &from->existence_lock))
         return commit_result(-L4_err::EInval);
 
@@ -481,7 +480,6 @@ Task::sys_unmap(Syscall_frame *f, Utcb *utcb)
       Ref_ptr<Task> self(this);
       Lock_guard<Lock> guard;
 
-      // FIXME: avoid locking the current task, it is not needed
       if (!guard.check_and_lock(&existence_lock))
         return commit_error(utcb, L4_error::Not_existent);