Regression - javax.servlet-api.jar shoud not be in WEB-INF/lib

In SOLR-15984, javax.servlet-api dependency was explicitly added to solr-core. This library is already included by Jetty, so has always existed in server/lib. Now after SOLR-15984, the servlet jar is also added to WEB-INF/lib causing smoketester to fail, as javax classes are forbidden in the distribution.

I have tried to remove this line again: https://github.com/apache/solr/commit/0ab2705f22553dc764c15fde47f927220e1c1d56#commitcomment-66617212 but then the build complains about usedUndeclaredArtifacts. 

Then I tried to make an exclusion permitUsedUndeclared 'javax.servlet:javax.servlet-api:3.1.0', but that seems to have no effect at all.

krisden