classes: kernel-balena: remove configuration warnings for 6.1

[alexgg]

• MEMCG_SWAP has been removed in v6.1 in 023223dfbfb34fcc
• NFSD_V3 is enabled by default since v5.18 in 5f9a62ff7d2808c
• 88EU_AP_MODE has been removed since v5.16 in 102243f893ecdef
• NFT_COUNTER has been removed since v5.17 in e6007b85dfa284c

Change-type: patch

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[alexgg]

@resin-jenkins retest this please

[alexgg]

@resin-jenkins retest this please