Do not ruin whole test runs because of uninstallable emacs

tests/Sanity/rebuild-systemtap/main.fmf

@@ -25,7 +25,6 @@ require+:
   - boost-devel
   - crash-devel
   - elfutils-devel
-  - emacs
   - gettext-devel
   - glibc
   - latex2html
@@ -37,6 +36,7 @@ require+:
   - systemtap
   - xmlto
 recommend:
+  - emacs
   - dyninst-devel
   - gtkmm24-devel
   - java-devel