tdf#160467 Remove z-index in prism code block

Right now code renders on top of header section.
Remove z-index to fix it.

Change-Id: Ic0cf226275eae1656107de27907a94af256d5555
Reviewed-on: https://gerrit.libreoffice.org/c/help/+/165768
Tested-by: Jenkins
Tested-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>
Reviewed-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>
(cherry picked from commit c89178e82abacbb240e571fcbd9bd0f76b40642d)
Reviewed-on: https://gerrit.libreoffice.org/c/help/+/165718
diff --git a/help3xsl/prism.css b/help3xsl/prism.css
index 4610909..54f0bf0 100644
--- a/help3xsl/prism.css
+++ b/help3xsl/prism.css
@@ -39,7 +39,6 @@ pre[class*="language-"] {

pre[class*="language-"] > code {
	position: relative;
	z-index: 1;
	border-left: 10px solid #358ccb;
	box-shadow: -1px 0px 0px 0px #358ccb, 0px 0px 0px 1px #dfdfdf;
	background-color: #fdfdfd;