Undefined name 'dla' in models/networks/dlav0.py

[cclauss]

https://github.com/ifzhang/FairMOT/blob/master/src/lib/models/networks/dlav0.py#L417

flake8 testing of https://github.com/ifzhang/FairMOT on Python 3.8.1

$ flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics

./src/lib/models/networks/dlav0.py:417:5: F821 undefined name 'dla'
    dla.BatchNorm = bn
    ^
1     F821 undefined name 'dla'
1

https://flake8.pycqa.org/en/latest/user/error-codes.html

On the flake8 test selection, this PR does not focus on "style violations" (the majority of flake8 error codes that psf/black can autocorrect). Instead these tests are focus on runtime safety and correctness:

• E9 tests are about Python syntax errors usually raised because flake8 can not build an Abstract Syntax Tree (AST). Often these issues are a sign of unused code or code that has not been ported to Python 3. These would be compile-time errors in a compiled language but in a dynamic language like Python they result in the script halting/crashing on the user.
• F63 tests are usually about the confusion between identity and equality in Python. Use ==/!= to compare str, bytes, and int literals is the classic case. These are areas where a == b is True but a is b is False (or vice versa). Python >= 3.8 will raise SyntaxWarnings on these instances.
• F7 tests logic errors and syntax errors in type hints
• F82 tests are almost always undefined names which are usually a sign of a typo, missing imports, or code that has not been ported to Python 3. These also would be compile-time errors in a compiled language but in Python a NameError is raised which will halt/crash the script on the user.

[ifzhang]

We do not use the model dlav0 and I will delete the error, so you can just ignore it.