clean up `setup.py` -- `VERSION_GE_1_1/3/5`

[crcrpar]

I think we'd be able to comfortably remove these variables:

apex/setup.py

Lines 125 to 139 in 2eda0ac

	# Set up macros for forward/backward compatibility hack around
	# https://github.com/pytorch/pytorch/commit/4404762d7dd955383acee92e6f06b48144a0742e
	# and
	# https://github.com/NVIDIA/apex/issues/456
	# https://github.com/pytorch/pytorch/commit/eb7b39e02f7d75c26d8a795ea8c7fd911334da7e#diff-4632522f237f1e4e728cb824300403ac
	version_ge_1_1 = []
	if (TORCH_MAJOR > 1) or (TORCH_MAJOR == 1 and TORCH_MINOR > 0):
	version_ge_1_1 = ["-DVERSION_GE_1_1"]
	version_ge_1_3 = []
	if (TORCH_MAJOR > 1) or (TORCH_MAJOR == 1 and TORCH_MINOR > 2):
	version_ge_1_3 = ["-DVERSION_GE_1_3"]
	version_ge_1_5 = []
	if (TORCH_MAJOR > 1) or (TORCH_MAJOR == 1 and TORCH_MINOR > 4):
	version_ge_1_5 = ["-DVERSION_GE_1_5"]
	version_dependent_macros = version_ge_1_1 + version_ge_1_3 + version_ge_1_5

rel:

• Allow env vars to specify custom extensions to build #1910