Make MemTraceDriver no longer be UnitTestModule

This makes it trickier to hook the driver up to sbus since we need to
assert its io.start.  We still need io.finished coming out of it to tell
when the trace finished.

src/main/scala/tilelink/Coalescing.scala

@@ -1362,8 +1362,11 @@ class MemTraceDriverImp(
     config: CoalescerConfig,
     filename: String,
     traceHasSource: Boolean
-) extends LazyModuleImp(outer)
+) extends LazyModuleImp(outer) {
-    with UnitTestModule {
+  val io = IO(new Bundle {
+    val finished = Output(Bool())
+  })
+
   // Current cycle mark to read from trace
   val traceReadCycle = RegInit(1.U(64.W))
 
@@ -2005,7 +2008,7 @@ class TLRAMCoalescerLogger(filename: String)(implicit p: Parameters)
 
   lazy val module = new Impl
   class Impl extends LazyModuleImp(this) with UnitTestModule {
-    driver.module.io.start := io.start
+    // io.start is unused since MemTraceDriver doesn't accept io.start
     io.finished := driver.module.io.finished
 
     when(io.finished) {
@@ -2059,7 +2062,7 @@ class TLRAMCoalescer(implicit p: Parameters) extends LazyModule {
 
   lazy val module = new Impl
   class Impl extends LazyModuleImp(this) with UnitTestModule {
-    driver.module.io.start := io.start
+    // io.start is unused since MemTraceDriver doesn't accept io.start
     io.finished := driver.module.io.finished
   }
 }