Remove duplicate global propagator setup in gRPC client example

[SyaoranY]

Fixes #4652

Changes

This PR removes the duplicate GlobalTextMapPropagator::SetGlobalPropagator() call from examples/grpc/client.cc.

The global HttpTraceContext propagator is already configured in InitTracer(), so the second setup in main() is redundant and may confuse users reading the example.

I tested the example after removing the duplicate call and observed no change in behavior.

No functional behavior is intended to change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.70%. Comparing base (e4232d8) to head (40eb226).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4654   +/-   ##
=======================================
  Coverage   86.70%   86.70%           
=======================================
  Files         525      525           
  Lines       20596    20596           
=======================================
  Hits        17856    17856           
  Misses       2740     2740           

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[lalitb]

Thanks.

[marcalff]

LGTM, thanks for the fix.