Bug 1108294 - Modernize AccEventGen.py; r=froydnj

I/O handling in AccEventGen.py is old school. Let's use context
managers. Let's also fix some minor style foo.

--HG--
extra : rebase_source : 70a2a7c344042e1ac187282fdda32cea194aa51b
Bug 1108294 - Removed unused cachedir option; r=froydnj

The argument isn't used. Let's remove dead code.

--HG--
extra : rebase_source : bd8d5f72c50b8820635de78f2548821b93e425ae
Bug 1108294 - Switch to argparse; r=froydnj

--HG--
extra : rebase_source : cc0b81afafbc2fa20f7327dda8f9c6e64c895386
Bug 1108294 - Use positional arguments; r=froydnj

There is only 1 caller to AccEventGen.py in the tree. We don't need
optional arguments. Convert them to positional.

Since the arguments are no longer optional, branches related to their
presence have been removed.

--HG--
extra : rebase_source : 35d51852dee031011ad9f079f3aba56b67948d7e
Bug 1108294 - Use mozbuild.makeutil for dependency file writing; r=froydnj

AccEventGen.py was using an old, one-off Python module for writing make
dependency files. We have a more appropriate API now. So we use it.

While we were here, we modified file writing to use FileAvoidWrite to
avoid always writing the output files and bumping mtimes.

--HG--
extra : rebase_source : 34ef9badacceb4791f27816c756ad9c95bf4069c
Bug 1108294 - Removed unused makeutils Python module; r=froydnj

There are no more consumers of makeutils.py in the tree. So we delete
it.

--HG--
extra : rebase_source : bf19cdf722027758161e588395464da83fc2c37c
Bug 1108294 - Remove python/codegen from virtualenv; r=froydnj

The python/codegen directory is empty. Remove it from the virtualenv.

--HG--
extra : rebase_source : 975806cc506631b2174c6b0304973923eda9f766