LGTM.com - py/similar-function might be too sensitive

**Description of the false positive**

The two functions *are* similar, so I hesitate to call this a true "false positive".

But the differences are substantial enough—variations in which SQLAlchemy table is queried, which columns are used in filters, which object properties are needed, etc.—that trying to write a single function to do both jobs would (arguably) be a bigger code smell than this.

It's also worth noting that there are other pairs of functions (the `set` and `get` companions in each suite for `nick` and `channel`) _not_ marked as similar, even though they're no more or less so than the `delete` functions that were detected. And there's another suite of also-similar `plugin` functions that weren't flagged by the analysis.

**URL to the alert on the project page on LGTM.com**

https://lgtm.com/projects/g/sopel-irc/sopel/snapshot/f6d393044ee7c7f1a7ba6fe0c4e8a152eb5948b2/files/sopel/db.py?sort=name&dir=ASC&mode=heatmap#x9fad0d3c3a380402:1