Allow implicit conversions for NN errors -- hal

This change allows GeneralErrors to be created from a string and allows
ExecutionErrors to be created from a string or a GeneralError.
This makes error handling more terse, removing the need for helper
functions such as makeGeneralFailure or makeExecutionFailure.

Bug: N/A
Test: mma
Change-Id: I8c5e80a2eb4f399fad64aab763fe6fa08cf8d1db
diff --git a/neuralnetworks/1.2/utils/src/Callbacks.cpp b/neuralnetworks/1.2/utils/src/Callbacks.cpp
index 9f54bb1..01b5e12 100644
--- a/neuralnetworks/1.2/utils/src/Callbacks.cpp
+++ b/neuralnetworks/1.2/utils/src/Callbacks.cpp
@@ -75,8 +75,7 @@
                << "execution failed with " << toString(status);
     }
     HANDLE_HAL_STATUS(status) << "execution failed with " << toString(status);
-    return hal::utils::makeExecutionFailure(
-            convertExecutionGeneralResultsHelper(outputShapes, timing));
+    return convertExecutionGeneralResultsHelper(outputShapes, timing);
 }
 
 Return<void> PreparedModelCallback::notify(V1_0::ErrorStatus status,