phosphor-ipmi-blobs-binarystore: Code Health Cleanup

Removed the following warning.
- using decl '*' is unused in unit tests

```
binarystore.hpp:58:5: style: Class 'BinaryStore' has a constructor with 1 argument that is not explicit. [noExplicitConstructor]
    BinaryStore(std::unique_ptr<SysFile> file, bool readOnly = false,
    ^
test/fake_sys_file.hpp:29:5: style: Class 'FakeSysFile' has a constructor with 1 argument that is not explicit. [noExplicitConstructor]
    FakeSysFile(const std::string& s) : data_(s)
    ^
binarystore.cpp:164:16: style: Consider using std::transform algorithm instead of a raw loop. [useStlAlgorithm]
        result.push_back(blob.blob_id());
               ^
test/binarystore_unittest.cpp:50:5: style: Class 'SysFileBuf' has a constructor with 1 argument that is not explicit. [noExplicitConstructor]
    SysFileBuf(std::string* storage) : data_{storage}
    ^
test/handler_unittest.cpp:161:35: style: Variable 'staleBaseId' is assigned a value that is never used. [unreadVariable]
    const std::string staleBaseId = "/stale/"s;
```

Change-Id: I3f6e10ee3a89ec745a601dc488a75277b33c83fb
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/test/binarystore_unittest.cpp b/test/binarystore_unittest.cpp
index 2a00696..f7c8a8e 100644
--- a/test/binarystore_unittest.cpp
+++ b/test/binarystore_unittest.cpp
@@ -47,7 +47,7 @@
 class SysFileBuf : public binstore::SysFile
 {
   public:
-    SysFileBuf(std::string* storage) : data_{storage}
+    explicit SysFileBuf(std::string* storage) : data_{storage}
     {
     }