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/bridges/class.kt

@@ -0,0 +1,13 @@
+// FIR_IDENTICAL
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+// TARGET_BACKEND: JVM_IR
+
+open class B<T> {
+    open fun foo(t: T) {}
+}
+
+class C : B<String>() {
+    override fun foo(t: String) {}
+
+    <!ACCIDENTAL_OVERRIDE!>fun foo(o: Any)<!> {}
+}