Don't run net_4_0 tests during "make check"

As @marek-safar noted in mono@cf4f10e#commitcomment-7128403, the IL code for the 4.0 profile is never used
for running (the assemblies are just built for having metadata), so it makes no sense to execute 4.0 tests during "make check"
Merge pull request #1180 from akoeplinger/no-net40-in-make-check

Don't run net_4_0 tests during "make check"