Fix #440, Replaces inaccurate CF_CFDP_ReceiveMessage comment

[chillfig]

Checklist (Please check before submitting)

• [x] I reviewed the Contributing Guide.
• [x] I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fixes #440, Replaces inaccurate comment regarding not getting output buffer within CF_CFDP_ReceiveMessage().

Testing performed Manual inspection

Expected behavior changes No impact to behavior

System(s) tested on

• OS:Ubuntu 20.04

Additional context N/A

Third party code N/A

Contributor Info - All information REQUIRED for consideration of pull request Justin Figueroa, Vantage Systems