Remove use of RUSTC_COMPILETEST env var

Author: bjorn3

src/librustc_trans_utils/trans_crate.rs

@@ -279,8 +279,6 @@ impl TransCrate for MetadataOnlyTransCrate {
         sess.abort_if_errors();
         if !sess.opts.crate_types.contains(&CrateType::CrateTypeRlib)
             && !sess.opts.crate_types.contains(&CrateType::CrateTypeDylib)
-            // Don't error when running under compiletest
-            && ::std::env::var("RUSTC_COMPILETEST") != Ok("1".to_string())
         {
             sess.fatal("Executables are not supported by the metadata-only backend.");
         }

src/tools/compiletest/src/runtest.rs

@@ -1278,7 +1278,7 @@ impl<'test> TestCx<'test> {
             TargetLocation::ThisFile(self.make_exe_name()),
         );
 
-        rustc.arg("-L").arg(&self.aux_output_dir_name()).env("RUSTC_COMPILETEST", "1");
+        rustc.arg("-L").arg(&self.aux_output_dir_name());
 
         match self.config.mode {
             CompileFail | Ui => {