Remove hack to fix iconv discovery

Cmake builds of qtbase at least don't have the problem this hack tried
to fix.

minicoin/minicoin.yml

@@ -36,9 +36,6 @@ machines:
       - role: linux-desktop
         desktop: lxde
       - role: linux-builder
-        # libiconv is missing on ubuntu20.04, so remove header as well
-      - role: script
-        script: "rm -f /usr/include/iconv.h"
 
   - name: centos8
     box: generic/centos8