Slightly misleading description of IsDeleted

[avelanarius]

The documentation for IsDeleted can be slightly misleading:

scylla-cdc-go/change.go

Lines 352 to 353 in 0bde107

	// IsDeleted returns a boolean indicating if given column was set to null.
	// This only works for clustering columns.

1. "This only works for clustering columns." - clustering columns of the base table
2. "boolean indicating if given column was set to null" - in non-frozen collections, IsDeleted=true means that a collection was overwritten, not necessarily set to null.

(I'm in process of writing the same docstring for a corresponding method in Java library and also having difficulty to word it properly - succinctly, but remembering all those corner cases...)

[avelanarius]

My try at documenting IsDeleted method in Java:

scylladb/scylla-cdc-java@c085d36