docs(readme): remove dev.ini reference (#8419)

remove dev.ini reference as it seems not working anymore.

README.md

@@ -146,8 +146,7 @@ Create a custom.ini in the conf directory to override default configuration opti
 You only need to add the options you want to override. Config files are applied in the order of:
 
 1. grafana.ini
-2. dev.ini (if found)
-3. custom.ini
+1. custom.ini
 
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