ECMWF MACC will be retired

[mikofski]

Is your feature request related to a problem? Please describe.
ECMWF is retiring MACC and other public data sets, see: https://confluence.ecmwf.int/display/DAC/Decommissioning+of+ECMWF+Public+Datasets+Service

Describe the solution you'd like
remove the get_ecmwf() functions from iotools

Describe alternatives you've considered
find out where the data sets will be archived? tell users to use alternate tools?

Additional context
https://confluence.ecmwf.int/display/DAC/Decommissioning+of+ECMWF+Public+Datasets+Service