Revert "Set crosvm as the default VMM for cuttlefish"

This reverts commit 43b39d625bc6301b379bcc75f6e0dc7d699666a7.

Reason for revert: b/132986546

Change-Id: I2616a9de2d4fd46795630a9fbb7a181f834166da
diff --git a/host/commands/launch/flags.cc b/host/commands/launch/flags.cc
index 6c0867d..b1877d2 100644
--- a/host/commands/launch/flags.cc
+++ b/host/commands/launch/flags.cc
@@ -85,7 +85,7 @@
 DEFINE_string(instance_dir, "", // default handled on ParseCommandLine
               "A directory to put all instance specific files");
 DEFINE_string(
-    vm_manager, vm_manager::CrosvmManager::name(),
+    vm_manager, vm_manager::QemuManager::name(),
     "What virtual machine manager to use, one of {qemu_cli, crosvm}");
 DEFINE_string(
     gpu_mode, vsoc::kGpuModeGuestSwiftshader,