routing: un-deprecate legacy delegated routing API

[gammazero]

Since IPIP-378 is not moving forward, the legacy API is not deprecated because there nothing to replace it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.11%. Comparing base (23312e7) to head (98e62c3).
⚠️ Report is 5 commits behind head on main.

@@           Coverage Diff           @@
##             main    #1075   +/-   ##
=======================================
  Coverage   61.10%   61.11%           
=======================================
  Files         264      264           
  Lines       26215    26215           
=======================================
+ Hits        16019    16021    +2     
  Misses       8519     8519           
+ Partials     1677     1675    -2     

Files with missing lines	Coverage Δ
routing/http/server/server.go	76.15% <ø> (ø)

... and 12 files with indirect coverage changes

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[lidel]

After discussing with @aschmahmann and @gammazero we decided to keep this deprecated.

My thinking is: close this, and instead update godoc in #1076 to reference more relevant IPIP.

Thoughts?

[gammazero]

Thoughts?

... Closing