Remove friend classes and clean up write functions in NodeColumn

[benjaminwinger]

A few things I noticed could be cleaned up.

• NodeColumn::write(ValueVector* nodeIDVector, ValueVector* vectorToWriteFrom) was only used in a function which was removed.
• The remaining write function was equivalent to writeInternal, and there didn't really seem to be much of a reason to have that be protected.
• The four NodeColumn friend classes were just using fields which are otherwise exposed by public functions (or could be, in the case of getMetadata and write)
• Removed a couple of unused headers.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (3fe7e20) 89.71% compared to head (ffecf29) 89.73%.

❗ Current head ffecf29 differs from pull request most recent head 34e4b96. Consider uploading reports for the commit 34e4b96 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2240      +/-   ##
==========================================
+ Coverage   89.71%   89.73%   +0.01%     
==========================================
  Files        1012     1012              
  Lines       35919    35898      -21     
==========================================
- Hits        32226    32214      -12     
+ Misses       3693     3684       -9     

Files	Coverage Δ
src/include/storage/local_table.h	100.00% <100.00%> (ø)
src/include/storage/store/node_column.h	100.00% <100.00%> (ø)
src/storage/local_table.cpp	94.22% <100.00%> (+0.02%)	⬆️
src/storage/store/node_column.cpp	84.38% <100.00%> (+5.25%)	⬆️
src/storage/store/struct_node_column.cpp	87.80% <100.00%> (ø)

... and 5 files with indirect coverage changes

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