Simplify Executor.getSpawnActionContext() by removing mnemonic: spawn is enough.

RELNOTES: None
PiperOrigin-RevId: 190544948
diff --git a/src/main/java/com/google/devtools/build/lib/exec/SymlinkTreeHelper.java b/src/main/java/com/google/devtools/build/lib/exec/SymlinkTreeHelper.java
index 612b926..5f231e4 100644
--- a/src/main/java/com/google/devtools/build/lib/exec/SymlinkTreeHelper.java
+++ b/src/main/java/com/google/devtools/build/lib/exec/SymlinkTreeHelper.java
@@ -124,7 +124,7 @@
               shellEnvironment,
               inputManifestArtifact);
       return actionExecutionContext
-          .getSpawnActionContext(owner.getMnemonic(), spawn)
+          .getSpawnActionContext(spawn)
           .exec(spawn, actionExecutionContext);
     } else {
       // Pretend we created the runfiles tree by copying the manifest