Remove otel-instrument-est wraper (#103)

*Issue #, if available:*

*Description of changes:*
Follow changes on
#101.

Instead of using a `otel-instrument-esm` wrapper which is redudent, we
will have customer to use `HANDLER_IS_ESM` env var to enforce ESM
instrumentation for the failed to detected cases.

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Author: mxiamxia

lambda-layer/packages/layer/scripts/otel-instrument

@@ -1,5 +1,5 @@
 #!/bin/bash
-isESMScript() {
+_is_esm_handler() {
   # Lambda function root directory
   TASK_DIR="/var/task"
 
@@ -28,7 +28,7 @@ isESMScript() {
   fi
 }
 
-if isESMScript; then
+if _is_esm_handler || [[ ${HANDLER_IS_ESM} == true ]]; then
   export NODE_OPTIONS="${NODE_OPTIONS} --import @aws/aws-distro-opentelemetry-node-autoinstrumentation/register --experimental-loader=@opentelemetry/instrumentation/hook.mjs"
   export HANDLER_IS_ESM=true
 else