fix: remove unnecessary line [skip ci]

oesteban · effigies · commit 0ce15de2f6a6 · 2020-01-06T10:42:38.000-05:00
diff --git a/doc/Makefile b/doc/Makefile
@@ -5,7 +5,6 @@
 SPHINXOPTS    =
 SPHINXBUILD   = sphinx-build
 PAPER         =
-PYTHONPATH    = $(PWD)
 
 # Internal variables.
 PAPEROPT_a4     = -D latex_paper_size=a4
