A few view functions were taking a Tx, which had to be shard-specific,
but that's sort of awkward -- the view is inherently not shard-specific,
so it should be handling sharding internally.
There were also a couple of remaining obsolete checks for whether a
Tx was nil, at least two of which were in contexts where it absolutely
can't be. Remove all of them, and also the function itself.
The "field/view will just synthesize a tx" behavior is awful and
also hides a number of fundamental flaws. We distinguish between
"we really do mean to work on a single shard here" and "we intend
to work on the whole field or view", and the latter now take
Qcx instead of Tx.
This eliminates a lot of very weird cases where we checked for
nil Tx and synthesized them, and also gets us away from
field and view taking Tx parameters when no possible Tx
can be constructed which is valid, because Tx are inherently
shard-specific at this time.
* removes unused filesize function
* removes ioutil usage
* updates ioutil.ReadAll to io.ReadAll
* updates ioutil.TempFile to os.CreateTemp
* updates ioutil.TempDir to os.MkdirTemp
* updates ioutil.ReadAll to os.ReadAll
* update ioutil.WriteFile to os.WriteFile
* updates ioutil.Discard to io.Discard
* updates ioutil.ReadDir to os.ReadDir where applicable
* removes unused code in idk
* creates type to use for context value keys
* replaces assert.Nil with assert.NoError for error checks
