Removing deprecated chunk storage flag

[alanprot]

What this PR does:
Removing deprecated chunk storage flag.

This flag was used on chunk storage but we removed chunk storage 2 releases ago.

Which issue(s) this PR fixes:
Fixes #

Checklist

• [NA] Tests updated
• Documentation added
• [NA] CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[yeya24]

THanks, just need to fix lint

[friedrichg]

ok  	github.com/cortexproject/cortex/pkg/configs/userconfig	1.037s
--- FAIL: TestLoadRuntimeConfig_ShouldLoadAnchoredYAML (0.00s)
    runtime_config_test.go:33: 
        	Error Trace:	/__w/cortex/cortex/pkg/cortex/runtime_config_test.go:33
        	Error:      	Received unexpected error:
        	            	yaml: unmarshal errors:
        	            	  line 9: field max_series_per_query not found in type validation.plain
        	            	  line 9: field max_series_per_query not found in type validation.plain
        	            	  line 9: field max_series_per_query not found in type validation.plain
        	Test:       	TestLoadRuntimeConfig_ShouldLoadAnchoredYAML

this error looks related