NEXUS-6569: NEXUS-5023: Fixes for std headers

Moving the IE one from ContentServlet to standard ones,
removing/replacing the misnamed header

Issue
https://issues.sonatype.org/browse/NEXUS-6569

Original PR
https://github.com/sonatype/nexus-oss/pull/525

CI
http://bamboo.s/browse/NX-OSSF53