Remove duplicative FINEST-level error logging in GrpcExporter

The onError method logged failures at SEVERE (with the exception)
and again at FINEST (manually printing the exception via toString).
The FINEST log is redundant since any logging framework can render
the stack trace from the exception already included in the SEVERE
log.

Resolves #8098

Author: VamshikrishnaMonagari

exporters/common/src/main/java/io/opentelemetry/exporter/internal/grpc/GrpcExporter.java

@@ -132,9 +132,6 @@ private void onError(
             + "s. The request could not be executed. Error message: "
             + e.getMessage(),
         e);
-    if (logger.isLoggable(Level.FINEST)) {
-      logger.log(Level.FINEST, "Failed to export " + type + "s. Details follow: " + e);
-    }
     result.failExceptionally(FailedExportException.grpcFailedExceptionally(e));
   }