Network alias is conflicting with the module names

[wyli]

Describe the bug
some network modules can't be imported, due to incorrect alias settings.

To Reproduce

import monai.networks.nets.densenet as mod
print(type(mod))

The outcome is <class 'type'>.

Expected behavior
The outcome should be <class 'module'>, because monai/networks/nets/densenet.py is a file.

Additional context
for example

MONAI/monai/networks/nets/densenet.py

Line 393 in ff08334

Densenet = densenet = DenseNet

the alias name densenet is conflicting with the file name monai/networks/nets/densenet.py.