TransRead: remove local caching functionality

TransRead: remove local caching functionality

Remove the local caching functionality of the TransRead module. This
functionality does not really belong to the module, and it only makes things
more complex. It is better to either make users of TransRead to locally cache
remote files, or create a small wrapper over TransRead for these purposes.

Since currently there is only one user of this functionality, we just implement
local caching in bmaptool directly.

Change-Id: I649a5e761b9bc4b6b10d035bfd790357eaf6c373
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>