Remove support for otel.java.experimental.exporter.memory_mode

[jack-berg]

The new otel.java.exporter.memory_mode has been available sine 1.44.0, and there have been 3 minor releases since.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.85%. Comparing base (0465c79) to head (3369ca0).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #7127      +/-   ##
============================================
- Coverage     89.85%   89.85%   -0.01%     
+ Complexity     6613     6610       -3     
============================================
  Files           740      740              
  Lines         19991    19986       -5     
  Branches       1966     1964       -2     
============================================
- Hits          17963    17958       -5     
  Misses         1439     1439              
  Partials        589      589              

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