Deprecate CRS2 Extension

[jyutzler]

@KRyden has asked the SWG to investigate replacing the values for the definition column from the gpkg_spatial_ref_sys table with WKT2 encoding since software is now widely available to support the new encoding. (This was not the case in 2014.)

This would make the WKT for CRS Extension obsolete.

According to Keith, this version of WKT2 contains a superset of WKT1 so we would be fine from a forwards-compatibility perspective. However, there is a reverse-compatibility risk if a 1.3 GeoPackage were opened by a client that was unaware of WKT2 and the "definition" column contained WKT2. This may be enough of a breaking change to cause a major revision.

Perhaps the clause after R117 is sufficient and this is not necessary.

If, for a particular row, both the definition and definition_12_063 columns are populated, the value in the definition_12_063 column takes priority.