Removing some of these assets can result in a broken Landscape Editor (Engine crash on landscape editor load)
The temp fix im using right now is simple and listed below, go into the source, find and nuke the reference, these assets have no impact on my editor / packaged build when the edits below are performed, im not entirely sure but i assume Landmass plugin auto references these, i dont even need that plugin itself, only need it to use the Water plugin, kinda messy atm (im using 5.4) but the simple fixes below work in Editor & Packaged build (shipping)
Just go back into the /All folder, make sure you have plugins/engine content visible, then search for these assets:
/BrushBounds
Open it
Remove ALL TilingAA* nodes
/M_BrushSprite_01
Open material
Find the S_Terrain texture sample
OPTIONAL: You might have issues with these, or you might not:
/UnicolorCarpaint
Open the material
Locate T_ShapeNormal texture
Delete or replace
/C4DReference
Open the material
Find the WhiteSquareTexture reference
Delete or replace