Disable deprecated linters - structcheck, deadcode, varcheck, ifshort

[killianmuldoon]

The following linters are deprecated in golangci-lint but we're still using them in our config:

• structcheck - Finds unused struct fields
• deadcode - Finds unused code
• varcheck - Finds unused global variables and constants
• ifshort - Go linter that checks if your code uses short syntax for if-statements whenever possible.

We should remove these linters at some point as they're no longer mantained, but is there a strong reason to keep any of them around?

I think ifshort is low-impact and is currently buggy (gives different results on my machine for some reason). The others - deadcode, varcheck, and struct check can all be replaced by unused

[killianmuldoon]

/kind cleanup

[killianmuldoon]

/assign

[killianmuldoon]

I've removed the linters in #7114 to see if it's desirable / if there's any objections.

[chrischdi]

I'd 👍 for making use of unused. These linters sound helpful for imho.

A buggy / non-deterministic ifshort makes no sense for me.

[sbueringer]

+1 to drop them

[fabriziopandini]

+1 to drop them given that we are already running the unused linter

[fabriziopandini]

/triage accepted

[killianmuldoon]

dropped in #7114

/close