Re-enable libsnapshot ImageManagerTest

ImageManagerTest had been temporarily disabled because flaky.
This test looks stable now, re-enable it.

Bug: 148889015
Test: atest vts_libsnapshot_test [-- --abi x86]
Signed-off-by: Alessio Balsini <balsini@google.com>
Change-Id: I858661fed7f58d1e2857ed88f5d8e0f5220bf8c2
(cherry picked from commit 42a608162d)
Merged-In: I858661fed7f58d1e2857ed88f5d8e0f5220bf8c2

fs_mgr/libsnapshot/snapshot_test.cpp

@@ -1799,7 +1799,6 @@ class ImageManagerTest : public SnapshotTest, public WithParamInterface<uint64_t
   protected:
     void SetUp() override {
         if (!is_virtual_ab_) GTEST_SKIP() << "Test for Virtual A/B devices only";
-        GTEST_SKIP() << "WIP failure b/149738928";
 
         SnapshotTest::SetUp();
         userdata_ = std::make_unique<LowSpaceUserdata>();