Change Metadata#create()/update()/delete() fn from async to sync

These fns were in async call (i.e. polling) in 1.1 or ealier, and became deprecated in ver. 1.2. Now from ver 1.3, they will be used as sync method calls (i.e. request/response to get the result) as other apis.
The change is disruptive when the app code is using jsforce less than ver. 1.1.