Remove dependence on rusqlite

[marcua]

Now that we use sqlite via sqlx, the underlying library dependencies conflict. Additionally, we don't want different libraries for sqlite in hosted DBs vs metadata DBs.

Error (that we get around for now by downgrading to rusqlite 0.27.0):

error: failed to select a version for `libsqlite3-sys`.
    ... required by package `sqlx-core v0.6.3`
    ... which satisfies dependency `sqlx-core = "^0.6.3"` (locked to 0.6.3) of package `sqlx v0.6.3`
    ... which satisfies dependency `sqlx = "^0.6.3"` (locked to 0.6.3) of package `ayb v0.1.3 (/home/marcua/ayb)`
versions that meet the requirements `^0.24.1` are: 0.24.2, 0.24.1

the package `libsqlite3-sys` links to the native library `sqlite3`, but it conflicts with a previous package which links to `sqlite3` as well:
package `libsqlite3-sys v0.26.0`
    ... which satisfies dependency `libsqlite3-sys = "^0.26.0"` (locked to 0.26.0) of package `rusqlite v0.29.0`
    ... which satisfies dependency `rusqlite = "^0.29.0"` (locked to 0.29.0) of package `ayb v0.1.3 (/home/marcua/ayb)`
Only one package in the dependency graph may specify the same links value. This helps ensure that only one copy of a native library is linked in the final binary. Try to adjust your
 dependencies so that only one package uses the links ='libsqlite3-sys' value. For more information, see https://doc.rust-lang.org/cargo/reference/resolver.html#links.