modify-python-lldb.py: (Re)move __len__ and __iter__ support

Summary:
This patch moves the modify-python-lldb code for adding new functions to
the SBModule class into the SBModule interface file. As this is the last
class using this functionality, I also remove all support for this kind
of modifications from modify-python-lldb.py.

Reviewers: amccarth, clayborg, jingham

Subscribers: zturner, lldb-commits

Differential Revision: https://reviews.llvm.org/D60195

llvm-svn: 357680