Previously, we generated the SCons VariantDir directory name from the options. leading to huge paths. On some builders, this caused things to exceed system limits. As a workaround, we explicitly set a VARIANT_DIR Variable on the SCons invocation to override the auto generation.

However, in SERVER-17789, we changed the way that default variant directory creation worked, so that huge paths are no longer used.

All of the VARIANT_DIR= things in etc/evergreen.yml are therefore obsolete and can be removed.