Don't use temporary file for rustfmt fixer

rustfmt normally acts on a file in place, and applies configuration
from rustfmt.toml files according to the path of the file.

Using a temporary file for rustfmt breaks this functionality, so
removing the '%t' from the rustfmt command.

autoload/ale/fixers/rustfmt.vim

@@ -10,8 +10,6 @@ function! ale#fixers#rustfmt#Fix(buffer) abort
 
     return {
     \   'command': ale#Escape(l:executable)
-    \       . (empty(l:options) ? '' : ' ' . l:options)
-    \       . ' %t',
-    \   'read_temporary_file': 1,
+    \       . (empty(l:options) ? '' : ' ' . l:options),
     \}
 endfunction