Remove duplicate import

Author: fortierq

Diff for: doc/python/3d-line-plots.md

@@ -37,15 +37,13 @@ jupyter:
 
 ```python
 import plotly.express as px
-import plotly.express as px
 df = px.data.gapminder().query("country=='Brazil'")
 fig = px.line_3d(df, x="gdpPercap", y="pop", z="year")
 fig.show()
 ```
 
 ```python
 import plotly.express as px
-import plotly.express as px
 df = px.data.gapminder().query("continent=='Europe'")
 fig = px.line_3d(df, x="gdpPercap", y="pop", z="year", color='country')
 fig.show()