Rename tests with diagnostics on JVM backend

Remove the "_ir" suffix. It was originally used to distinguish tests on
the JVM IR backend from the old JVM backend ("_old"), but the latter are
removed now.

compiler/testData/diagnostics/testsWithJvmBackend/duplicateJvmSignature/traitImpl/oneTrait.kt

@@ -0,0 +1,9 @@
+// FIR_IDENTICAL
+// TARGET_BACKEND: JVM_IR
+interface T {
+    fun getX() = 1
+}
+
+class C : T {
+    <!ACCIDENTAL_OVERRIDE!>val x<!> = 1
+}