nspr: remove non-executables from bin

Other package managers seem to remove these files as well.

Formula/nspr.rb

@@ -27,6 +27,9 @@ class Nspr < Formula
 
       system "make"
       system "make install"
+
+      (bin/'compile-et.pl').unlink
+      (bin/'prerr.properties').unlink
     end
   end
 end