docs: real-time: Fix duplicated sched(7) text

The man page reference appeared twice - once as plain text and
once as a hyperlink. Remove the plain text duplicate.

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260531141823.4118954-1-costa.shul@redhat.com>

Author: makelinux

Documentation/core-api/real-time/theory.rst

@@ -25,7 +25,7 @@ Scheduling
 ==========
 
 The core principles of Linux scheduling and the associated user-space API are
-documented in the man page sched(7)
+documented in the man page
 `sched(7) <https://man7.org/linux/man-pages/man7/sched.7.html>`_.
 By default, the Linux kernel uses the SCHED_OTHER scheduling policy. Under
 this policy, a task is preempted when the scheduler determines that it has