Remove dc_location_t

dc_location_t is an incomplete copy of _dc_location

The difference is that it lacks `int independent` field.
As a result, calloc did not allocate memory for this field.
deltachat-core (C version) has only one dc_location_t, that includes the last field.

src/dc_array.rs

@@ -1,4 +1,4 @@
-use crate::context::*;
+use crate::dc_location::_dc_location;
 use crate::dc_tools::*;
 use crate::types::*;
 use crate::x::*;