of: unittest: let dtc generate __local_fixups__

Remove the manually added __local_fixups__ because dtc can now generate
them. This also fixes a new warning in the process:

drivers/of/unittest-data/testcases.dtb: Warning (interrupts_extended_property): Could not get phandle node for /__local_fixups__/testcase-data/interrupts/interrupts-extended0:interrupts-extended(cell 3)
Signed-off-by: Rob Herring <robh@kernel.org>

drivers/of/unittest-data/testcases.dts

 /dts-v1/;
+/plugin/;
+
 / {
 	testcase-data {
 		changeset {
@@ -14,66 +16,3 @@ node-remove {
 #include "tests-match.dtsi"
 #include "tests-platform.dtsi"
 #include "tests-overlay.dtsi"
-
-/*
- * phandle fixup data - generated by dtc patches that aren't upstream.
- * This data must be regenerated whenever phandle references are modified in
- * the testdata tree.
- *
- * The format of this data may be subject to change. For the time being consider
- * this a kernel-internal data format.
- */
-/ { __local_fixups__ {
-	testcase-data {
-		phandle-tests {
-			consumer-a {
-				phandle-list = <0x00000000 0x00000008
-						0x00000018 0x00000028
-						0x00000034 0x00000038>;
-				phandle-list-bad-args = <0x00000000 0x0000000c>;
-			};
-		};
-		interrupts {
-			intmap0 {
-				interrupt-map = <0x00000004 0x00000010
-						 0x00000024 0x00000034>;
-			};
-			intmap1 {
-				interrupt-map = <0x0000000c>;
-			};
-			interrupts0 {
-				interrupt-parent = <0x00000000>;
-			};
-			interrupts1 {
-				interrupt-parent = <0x00000000>;
-			};
-			interrupts-extended0 {
-				interrupts-extended = <0x00000000 0x00000008
-						       0x00000018 0x00000024
-						       0x0000002c 0x00000034
-						       0x0000003c>;
-			};
-		};
-		testcase-device1 {
-			interrupt-parent = <0x00000000>;
-		};
-		testcase-device2 {
-			interrupt-parent = <0x00000000>;
-		};
-		overlay2 {
-			fragment@0 {
-				target = <0x00000000>;
-			};
-		};
-		overlay3 {
-			fragment@0 {
-				target = <0x00000000>;
-			};
-		};
-		overlay4 {
-			fragment@0 {
-				target = <0x00000000>;
-			};
-		};
-	};
-}; };