Removed memory leak in layer factory

[infomaniac777]

This PR addresses the following:

1. Using new for allocating a std::map is redundant and less idiomatic than allocating it directly on stack. The actual memory required for std::map will be allocated as per need basis from heap automatically.
2. Using new for a static pointer technically causes a memory leak here since delete is never really called for this.
   This change will address both these problems as stack objects are guaranteed to be freed on program termination.