Fix deprecation of Extract/Inject in otelgrpc

[nithinputhenveettil]

Fixes #7687

I tried running it locally using go run golang.org/x/pkgsite/cmd/pkgsite@latest -open in local, and everything looks fine to me.

[nithinputhenveettil]

@MrAlias : Since this deprecation was originally added 3 years ago, I’m not sure if it still needs to go in the CHANGELOG. What do you all think? I can add it if everyone feels it's necessary.

[MrAlias]

@MrAlias : Since this deprecation was originally added 3 years ago, I’m not sure if it still needs to go in the CHANGELOG. What do you all think? I can add it if everyone feels it's necessary.

+1 to adding an entry in the changelog under a ### Deprecated header in ## Unreleased.

It looks like the original included an entry, but it was not in the correct section header and we should try to announce it as much as possible now that tools are going to flag the functions.

[nithinputhenveettil]

@MrAlias: Agreed, I’ve added the entry to the CHANGELOG under the correct section.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.8%. Comparing base (b06b2a8) to head (673be11).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7689   +/-   ##
=====================================
  Coverage   78.7%   78.8%           
=====================================
  Files        186     186           
  Lines      14705   14705           
=====================================
+ Hits       11585   11591    +6     
+ Misses      2780    2776    -4     
+ Partials     340     338    -2     

Files with missing lines	Coverage Δ
...ogle.golang.org/grpc/otelgrpc/metadata_supplier.go	58.1% <ø> (ø)

... and 1 file with indirect coverage changes

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