remove redundant -W error pytest flag

It's now configured in pyproject.toml

Author: graingert

ci.sh

@@ -149,7 +149,7 @@ else
     # 'coverage xml' to generate the report that it uses, and that will only
     # apply the ignore patterns in the current directory's .coveragerc.
     cp ../.coveragerc .
-    if pytest -W error -r a --junitxml=../test-results.xml --run-slow ${INSTALLDIR} --cov="$INSTALLDIR" --verbose; then
+    if pytest -r a --junitxml=../test-results.xml --run-slow ${INSTALLDIR} --cov="$INSTALLDIR" --verbose; then
         PASSED=true
     else
         PASSED=false