Resolve "Support for icat "definition" field"

Closes #2792 (closed)

There are currently two places for the "technique name" when the ESRF data policy is enabled:

1. SCAN_SAVING.technique (obsolete)
2. the ICAT field "definition" which can be accessed for example by SCAN_SAVING.dataset.all.definition

Remove the obsolete SCAN_SAVING.technique as it stems from before we added ICAT metadata support in Bliss.

Note: do not confuse the following technique related things

1. The ICAT metadata field "definition" which seems to be used for the technique name in the dataset metadata (goes to ICAT)

   see SCAN_SAVING.dataset.all.definition

2. The ICAT technique related fields for technique related dataset metadata (goes to ICAT). This is related to Nexus application definitions but this is not actually saved in any HDF5 file (well it is in the garbage HDF5 file saved by the metadata manager tango server).

   see SCAN_SAVING.dataset.techniques and SCAN_SAVING.dataset.add_technique

3. The user scan metadata category "TECHNIQUE" for technique related scan metadata (goes to HDF5). This is basically a garbage dump of whatever the beamlines save in there (NXcollection). This is not related to Nexus application definitions.

   see bliss.scanning.scan_meta.ScanMeta