tree-wide: Convert to using autoptr(GString) vs g_string_free(...,TRUE)

tree-wide: Convert to using autoptr(GString) vs g_string_free(...,TRUE)

If we're freeing the segment, it's basically always better to use
`autoptr()`.  Fewer lines, more reliable, etc.

Noticed an instance of this in the pull code while reviewing a different PR,
decided to do a grep for it and fix it tree wide.

Closes: #836
Approved by: pwithnall