master: Remove unused code in filesystem.cc

This commit removes the following preprocessor directives:

  #define USE_FREENODE_BUCKETS 1
  #define USE_CUIDREC_BUCKETS 1
  #define EDGEHASH 1

and all the ifdefs which use them. It does not change anything that can
be observed by the C++ compiler. This is to prepare the code for adding
destructor of the metadata.

Change-Id: I3494e134b86ece95fab1124dbbada5e7231683a0