Backed out changeset cace4ffbecb2 (bug 1576030) requested by glandium

build/moz.configure/toolchain.configure

@@ -1902,11 +1902,6 @@ def cargo_incremental(opt_level, debug_rust, automation, code_coverage,
     if not enabled:
         return '0'
 
-    # Respect a forceful --enable-cargo-incremental even if we would otherwise
-    # disable it.
-    if enabled and enabled.origin != 'default':
-        return '1'
-
     # We never want to use incremental compilation in automation.  sccache
     # handles our automation use case much better than incremental compilation
     # would.