tree-wide: Switch tabs ⭾ in various files over to spaces ␠

As $DEITY intended.

I was reading the `prepare-root.c` code and the indentation damage was
distracting. Squash tabs that have leaked into various places in the code. I
didn't yet touch the `src/libostree` bits as that has higher potential for
conflict.

Closes: #852
Approved by: jlebon

src/rofiles-fuse/main.c

@@ -503,8 +503,7 @@ struct fuse_operations callback_oper = {
   .removexattr = callback_removexattr
 };
 
-enum
-{
+enum {
   KEY_HELP,
   KEY_VERSION,
 };