Python: Remove unneeded mutex

The mutex may potentially block concurrent calls to
Pip::infoImpl().

Make infoImpl() a static method in cpp.

Change-Id: I06e2de08674b5669e58684743d67a569da43d662
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/python/pipsupport.h

@@ -55,9 +55,6 @@ public:
 private:
     Pip(const Utils::FilePath &python);
 
-    PipPackageInfo infoImpl(const PipPackage &package);
-
-    QMutex m_lock;
     Utils::FilePath m_python;
 };