command/cliconfig: Remove remnant extraArg checks in provider_installation

In the first pass of implementing this it was strict about what arguments
are allowed inside source blocks, but that was counter to our usual design
principles for CLI config where we tend to ignore unrecognized things to
allow for some limited kinds of future expansion without breaking
compatibility with older versions of Terraform that will be sharing the
same CLI configuration files with newer versions.

However, I'd removed the tracking of that prior to the initial commit. I
missed some leftover parts when doing that removal, so this cleans up the
rest of it.

command/cliconfig/provider_installation.go

@@ -89,7 +89,6 @@ func decodeProviderInstallationFromConfig(hclFile *hclast.File) ([]*ProviderInst
 			sourceTypeStr := sourceBlock.Keys[0].Token.Value().(string)
 			var location ProviderInstallationSourceLocation
 			var include, exclude []string
-			var extraArgs []string
 			switch sourceTypeStr {
 			case "direct":
 				type BodyContent struct {
@@ -172,14 +171,6 @@ func decodeProviderInstallationFromConfig(hclFile *hclast.File) ([]*ProviderInst
 				continue
 			}
 
-			for _, argName := range extraArgs {
-				diags = diags.Append(tfdiags.Sourceless(
-					tfdiags.Error,
-					"Invalid provider_installation source block",
-					fmt.Sprintf("Invalid %s block at %s: this source type does not expect the argument %q.", sourceTypeStr, block.Pos(), argName),
-				))
-			}
-
 			pi.Sources = append(pi.Sources, &ProviderInstallationSource{
 				Location: location,
 				Include:  include,