fac942ca57dce6cfa5655a3ac8664d6a051bc01f test: Remove fragile assert_memory_usage_stable (MarcoFalke)
Pull request description:
This test fails on arm64 and a fuzz tests seems inappropriate for the functional test suite anyway, so remove it.
Example failures:
* https://travis-ci.org/bitcoin/bitcoin/jobs/611497963#L14517
* https://travis-ci.org/MarcoFalke/bitcoin-core/jobs/611029104#L3876
ACKs for top commit:
jamesob:
ACK fac942ca57
Tree-SHA512: 3577e7ce5891d221cb798454589ba796ed0c06621a26351bb919c23bc6bb46aafcd0b11cb02bbfde64b74d67cb2950da44959a7ecdc436491a34e8b045c1ccf4