Revert "Run externalisation by default."
Revert "Run externalisation by default."

This reverts commit 6c2c74bc0cc119d480d31183f2236518351281b5.

This is not useful yet.

mrakgr/futhark,HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,ihc/futhark,HIPERFIT/futhark,HIPERFIT/futhark,mrakgr/futhark,diku-dk/futhark,ihc/futhark,diku-dk/futhark,diku-dk/futhark,mrakgr/futhark,CulpaBS/wbBach,ihc/futhark