delete matplotlib (#28183)

Author: swtkiwi

python/requirements.txt

@@ -3,9 +3,7 @@ numpy>=1.13, <=1.16.4 ; python_version<"3.5"
 numpy>=1.13 ; python_version>="3.5"
 protobuf>=3.1.0
 gast==0.3.3
-matplotlib<=2.2.4 ; python_version<"3.6"
 scipy>=0.19.0, <=1.2.1 ; python_version<"3.5"
-matplotlib<=3.2.1 ; python_version>="3.6"
 scipy<=1.3.1 ; python_version=="3.5"
 scipy ; python_version>"3.5"
 rarfile