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/twoTraits.kt

@@ -0,0 +1,14 @@
+// FIR_IDENTICAL
+// TARGET_BACKEND: JVM_IR
+
+interface T1 {
+    fun getX() = 1
+}
+
+interface T2 {
+    val x: Int
+        get() = 1
+}
+
+class <!CONFLICTING_INHERITED_JVM_DECLARATIONS!>C<!> : T1, T2 {
+}