After bit of a play around with codes I found the solution. The change needs to be done in ToolbarFragment.jsp , which can be found in the directory of
"birt/viewer/org.eclipse.birt.report.viewer/birt/webcontent/birt/pages/control/ToolbarFragment.jsp"
comment out the following snippet and your are done :)
<%-- <TD WIDTH="15px">
<INPUT TYPE="image" NAME='parameter' SRC="birt/images/Report_parameters.gif"
TITLE="<%= BirtResources.getHtmlMessage( "birt.viewer.toolbar.parameter" )%>"
ALT="<%= BirtResources.getHtmlMessage( "birt.viewer.toolbar.parameter" )%>" CLASS="birtviewer_clickable">
</TD> --%>