Avoid error deleting selectseries field if it doesn't exist

[acwhite211]

Fixes #7098
Fixes #6942

Avoid issues on the test panel with the 0036_remove_spquery_selectseries migration due to the database state being off when it comes to the the selectseries field being present in the spquery table.

This was addressed for #7020, but needs to be done in a timely manner in the main branch.

Checklist

• Self-review the PR after opening it to make sure the changes look good and
  self-explanatory (or properly documented)
• Add relevant issue to release milestone
• Add a reverse migration if a migration is present in the PR

Testing instructions

• For dev testers, run all the migrations, through 0036_remove_spquery_selectseries . Make sure they run without error.
• For UX testing, open the QB viewer on the spquery table, and make sure that the "Select Series" field does not appear.

[emenslin]

• For UX testing, open the QB viewer on the spquery table, and make sure that the "Select Series" field does not appear.

Looks good

[grantfitzsimmons]

• For dev testers, run all the migrations, through 0036_remove_spquery_selectseries . Make sure they run without error.
• For UX testing, open the QB viewer on the spquery table, and make sure that the "Select Series" field does not appear.