Enabled simple-alias-mem-use.chpl under gasnet.

This test:
  test/distributions/robust/arithmetic/reindexing/simple-alias-mem-use.chpl
used to fail intermittently under gasnet.

The failure was represented by
  test/memory/vass/crash-memory-module-1.chpl
which was handled in r22223 aka 7209b2d a year ago.

I propose to enable simple-alias-mem-use.chpl under gasnet and see if it succeeds there consistently.