Update end child task error requirement (can't return error code from void function)

[skliper]

Is your feature request related to a problem? Please describe.
Calling CFE_ES_ExitChildTask from a main application task is a bug/error, but it's a void call so impossible to fully meet the ES: End Child Task - Error If Application Main Task,cES1314.1 as written since an error code can't be returned:

cFE/docs/cFE_FunctionalRequirements.csv

Line 116 in c4ae5b2

ES: End Child Task - Error If Application Main Task,cES1314.1,"If the calling task is the cFE Application Main Task, the cFE shall record the error in the System Log, and return an error code.",Cannot use Child Task Exit or Delete on the cFE Application Main Task.

Describe the solution you'd like
Remove the error code return language.

Describe alternatives you've considered
Add a return code. Really it's a bug so there's no use case to logically handle a return code when called from a main app context.

Additional context
None

Requester Info
Jacob Hageman - NASA/GSFC