Remove deprecated things

[grisumbras]

No description provided.

[cppalliance-bot]

An automated preview of the documentation is available at https://1040.jsondocs.prtest.cppalliance.org/libs/json/doc/html/index.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.40%. Comparing base (72b0e8a) to head (6d74dec).
Report is 17 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1040   +/-   ##
========================================
  Coverage    93.40%   93.40%           
========================================
  Files           87       87           
  Lines         8622     8622           
========================================
  Hits          8053     8053           
  Misses         569      569           

Files with missing lines	Coverage Δ
include/boost/json/detail/default_resource.hpp	83.33% <ø> (ø)
include/boost/json/detail/shared_resource.hpp	100.00% <ø> (ø)
include/boost/json/impl/value.ipp	99.12% <ø> (ø)
include/boost/json/monotonic_resource.hpp	100.00% <ø> (ø)
include/boost/json/result_for.hpp	100.00% <ø> (ø)
include/boost/json/static_resource.hpp	100.00% <ø> (ø)
include/boost/json/storage_ptr.hpp	100.00% <ø> (ø)
include/boost/json/string.hpp	100.00% <ø> (ø)
include/boost/json/value.hpp	98.83% <ø> (ø)
include/boost/json/value_to.hpp	100.00% <ø> (ø)

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[cppalliance-bot]

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