Remove obsolete sap flow sensors (quick fix)

[bpbond]

We can come up with a permanent fix for this later, but since the TEMPEST flood is next week, I just added a line of code to drop the sensors that no longer exist (SD2, CD6, SD9, CD10). See #32

[bpbond]

Hmm rather than worry about updating the test snapshot each time, I'm going to do it at the end of our updates if that's okay @stephpenn1 .

So for our PRs, make sure the test error is something like

── Failed tests ────────────────────────────────────────────────────────────────
Failure (test-shinytest2.R:8:3): {shinytest2} recording: TEMPESTdash
Snapshot of `file` to 'shinytest2/TEMPESTdash-001.json' has changed

That indicates that everything loaded and ran, but the dashboard is different than the saved test image (which we'll update after our changes are in).

[bpbond]

Merging, assuming this approach (above) is OK with SP