update rustc_index_macros feature handling

It seems that cargo can't conditionally propagate features
when `default-features` is set to `false`.

Signed-off-by: onur-ozkan <work@onurozkan.dev>

compiler/rustc_index/Cargo.toml

@@ -5,7 +5,7 @@ edition = "2021"
 
 [dependencies]
 # tidy-alphabetical-start
-rustc_index_macros = { path = "../rustc_index_macros", default-features = false }
+rustc_index_macros = { path = "../rustc_index_macros" }
 rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_serialize = { path = "../rustc_serialize", optional = true }
 smallvec = "1.8.1"

compiler/rustc_index_macros/Cargo.toml

@@ -12,5 +12,4 @@ proc-macro2 = "1"
 quote = "1"
 
 [features]
-default = ["nightly"]
 nightly = []