Remove cfeesugshellsrv section of users guide

[skliper]

Is your feature request related to a problem? Please describe.
ES shell command removed, documentation outdated.

Describe the solution you'd like
Clean documentation:

cFE/docs/src/cfe_es.dox

Lines 804 to 813 in fcaa1d0

	/**
	\page cfeesugshellsrv OS Shell
	NOTE: This cfe functionality is targeted for deprecation in favor of
	optionally including this capability via an application.
	Next: \ref cfeesugversion <BR>
	Prev: \ref cfeesugsyslogsrv <BR>
	Up To: \ref cfeesovr
	**/

and all references (fix Next/Prev)

Describe alternatives you've considered
None

Additional context
None

Requester Info
Jacob Hageman - NASA/GSFC