Fix license headers to only use a single /* comment to exclude it from doxygen

[dagardner-nv]

Prevents the license header from being repeatedly displayed as part of each namespace's documentation.

Discovered this while looking into nv-morpheus/Morpheus#837

[codecov]

Codecov Report

Merging #307 (1e8cfc0) into branch-23.07 (1509f6c) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@              Coverage Diff              @@
##           branch-23.07     #307   +/-   ##
=============================================
  Coverage         73.27%   73.27%           
=============================================
  Files               390      390           
  Lines             13353    13353           
  Branches           1006     1007    +1     
=============================================
  Hits               9785     9785           
  Misses             3568     3568           

Flag	Coverage Δ
cpp	69.10% <ø> (ø)
py	42.20% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...p/mrc/include/mrc/benchmarking/segment_watcher.hpp	55.79% <ø> (ø)
.../mrc/include/mrc/benchmarking/trace_statistics.hpp	100.00% <ø> (ø)
cpp/mrc/include/mrc/benchmarking/tracer.hpp	76.74% <ø> (ø)
cpp/mrc/include/mrc/channel/buffered_channel.hpp	47.61% <ø> (ø)
cpp/mrc/include/mrc/channel/channel.hpp	81.81% <ø> (ø)
cpp/mrc/include/mrc/channel/egress.hpp	100.00% <ø> (ø)
cpp/mrc/include/mrc/channel/ingress.hpp	100.00% <ø> (ø)
cpp/mrc/include/mrc/channel/null_channel.hpp	54.16% <ø> (ø)
cpp/mrc/include/mrc/channel/recent_channel.hpp	47.91% <ø> (ø)
cpp/mrc/include/mrc/codable/api.hpp	100.00% <ø> (ø)
... and 171 more

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[mdemoret-nv]

/merge