Revert accidental default collector type change.
Revert accidental default collector type change.

Default collector type had been changed to generational semi-space
by default by accident.

Change-Id: I060b3f292261b8bb258ca2a350e26a328340c49c

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst