res_odbc: Make pooling option deprecation notice more useful.

This changes the notice for the deprecation of the old
pooling options to point to the new option for doing
pooling. This gives a clearer direction as to what to
look into.

ASTERISK-26389 #close

Change-Id: I2ca9cdfdcd75aec170a7db9d5ff69a4cd25b7c10