Fix convect_shallow standard names to match spreadsheet

[jimmielin]

Originator(s): jimmielin

Description (include issue title and the keyword ['closes', 'fixes', 'resolves'] and issue number):

• minor update to convect_shallow standard names to match CCPP standard names spreadsheet's approved names

List all namelist files that were added or changed: N/A

List all files eliminated and why: N/A

List all files added and what they do: N/A

List all existing files that have been modified, and describe the changes:
(Helpful git command: git diff --name-status development...<your_branch_name>)
M schemes/hack_shallow/hack_convect_shallow.meta
M schemes/sima_diagnostics/convect_shallow_diagnostics.F90
M schemes/sima_diagnostics/convect_shallow_diagnostics.meta
update convect_shallow standard names

List all automated tests that failed, as well as an explanation for why they weren't fixed: N/A

Is this an answer-changing PR? If so, is it a new physics package, algorithm change, tuning change, etc? No - metadata only

If yes to the above question, describe how this code was validated with the new/modified features: N/A

[nusbaume]

Thanks @jimmielin!