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/fake_sys_file.hpp b/test/fake_sys_file.hpp
index eb8d024..1d319f6 100644
--- a/test/fake_sys_file.hpp
+++ b/test/fake_sys_file.hpp
@@ -26,7 +26,7 @@
     FakeSysFile()
     {
     }
-    FakeSysFile(const std::string& s) : data_(s)
+    explicit FakeSysFile(const std::string& s) : data_(s)
     {
     }