Define DEPTABLE's KEY_VERTEX as INTEGER PRIMARY KEY

Define DEPTABLE's KEY_VERTEX as INTEGER PRIMARY KEY

Summary:
This very small change decreases the size of the SQLite table by ~24% and improves the writing time in my very unscientific test by about 16%.

In SQLITE, INT is not the same as INTEGER. A table without an INTEGER PRIMARY KEY is created with a ROWID column. Specifying INTEGER PRIMARY KEY aliases ROWID to the user-created column. Additionally, [according to the SQLite documentation](https://www.sqlite.org/lang_createtable.html):

> Searching for a record with a specific rowid, or for all records with rowids within a specified range is around twice as fast as a similar search made by specifying any other PRIMARY KEY or indexed value.

At this time, this isn't terribly useful, because, as Jake pointed out to me, the cost of lookups is dwarved compared to the cost of reparsing and rechecking we do when looking up dependencies. I tested `--find-refs EntSchemaBase`, and the results were identical between the two states.

I suspect we defined the primary key as INT for DEPTABLE because INTEGER PRIMARY KEY used to be a 32-bit int and our KEY_VERTEX values were 64-bit. Our other tables define the primary key as INTEGER PRIMARY KEY already. The ROWID column is now also a 64-bit integer, so this change is safe. Again, [from the documentation](https://www.sqlite.org/autoinc.html):

> In SQLite, a column with type INTEGER PRIMARY KEY is an alias for the ROWID (except in WITHOUT ROWID tables) which is always a 64-bit signed integer

Reviewed By: ljw1004

Differential Revision: D10097554

fbshipit-source-id: d24fc7f64f03984520d1aa3ae9165918a2d3d006