get rustup home out of buck2 dirs

Author: nlopezgi

buck2/rust/BUCK

@@ -18,7 +18,7 @@ rust_library(
     env = select({
         "//platforms:engflow": {
             "RUSTUP_TOOLCHAIN":"/usr/local/rustup/toolchains/1.83.0-x86_64-unknown-linux-gnu",
-            "RUSTUP_HOME": "buck-out/.rustup",
+            "RUSTUP_HOME": ".rustup",
         },
         "DEFAULT": {},
     }),
@@ -37,7 +37,7 @@ rust_binary(
     env = select({
         "//platforms:engflow": {
             "RUSTUP_TOOLCHAIN":"/usr/local/rustup/toolchains/1.83.0-x86_64-unknown-linux-gnu",
-            "RUSTUP_HOME": "buck-out/.rustup",
+            "RUSTUP_HOME": ".rustup",
         },
         "DEFAULT": {},
     }),
@@ -62,7 +62,7 @@ rust_test(
     env = select({
         "//platforms:engflow": {
             "RUSTUP_TOOLCHAIN":"/usr/local/rustup/toolchains/1.83.0-x86_64-unknown-linux-gnu",
-            "RUSTUP_HOME": "buck-out/.rustup",
+            "RUSTUP_HOME": ".rustup",
         },
         "DEFAULT": {},
     }),