metric-config: remove the free-memory threshold

By default we have a metric on the available memory.  Free memory should
be a subset of available memory.  You can have some memory held by
kernel caches that can be evicted as needed, which show up in available
and not free.  Having a threshold on free memory is probably not what
anyone wants by default, so remove it from the default config.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I16d15266b6e10e6c7a788095b4b29d5e603e102c
2 files changed