Unquote backticks in sqlite identifiers

[JoeriAben]

Fixes #3350 Fixes #3684 Fixes #3800

In sqlite there is a quirky behavior where backticks are included in table and column names. This causes errors like relation "x" does not exist, even when the column or table is actually present.

The changes in this PR ensure that identifiers no longer include backticks as part of their names.

Steps to reproduce the issues this solves

schema.sql

CREATE TABLE `foo` (`bar` text);

queries.sql

-- name: GetFoo :many
SELECT bar FROM foo;

sqlc.yaml

version: "2"
sql:
  - engine: "sqlite"
    queries: "queries.sql"
    schema: "schema.sql"
    gen:
      go:
        package: "db"
        out: "db"

output

> sqlc generate    
# package db
queries.sql:1:1: relation "foo" does not exist

[fy0]

@kyleconroy please merge this PR, it's simple but solved a big problem for sqlite users.