Allow remove_column (now supported by SQLite)

From what I see, SQLite now supports `ALTER TABLE DROP COLUMN`: https://sqlite.org/lang_altertable.html#altertabdropcol

`remove_column` would probably look like this then?
```julia
function SearchLight.Migration.remove_column(table_name::Union{String,Symbol},
name::Union{String,Symbol}, options::Union{String,Symbol} = "") :: Nothing
SearchLight.query("ALTER TABLE `$table_name` DROP COLUMN `$name` $options")

nothing
end
```

I am very new to database stuff; maybe the possible failures reasons (like column being unique, or an index) should be checked in the function?