v.db.dropcolumn drops a column from the attribute table connected
to a given vector map. It automatically checks the connection for the specified
layer. v.db.dropcolumn omits to delete the 'cat' column which is
relevant to keep the connection between vector map and table.
NOTES
v.db.dropcolumn is a front-end to db.execute to allow easier usage.
The existing database connection(s) can be verified with v.db.connect.