simplify severityFromString

Author: lobsterkatie

packages/utils/src/severity.ts

@@ -2,21 +2,14 @@ import { Severity, SeverityLevel } from '@sentry/types';
 
 export const validSeverityLevels = ['fatal', 'error', 'warning', 'log', 'info', 'debug', 'critical'];
 
-function isSupportedSeverity(level: string): level is Severity {
-  return validSeverityLevels.indexOf(level as SeverityLevel) !== -1;
-}
 /**
  * Converts a string-based level into a {@link Severity}.
  *
  * @param level string representation of Severity
  * @returns Severity
  */
 export function severityFromString(level: SeverityLevel | string): Severity {
-  if (level === 'warn') return Severity.Warning;
-  if (isSupportedSeverity(level)) {
-    return level;
-  }
-  return Severity.Log;
+  return (level === 'warn' ? Severity.Warning : validSeverityLevels.includes(level) ? level : Severity.Log) as Severity;
 }
 
 // TODO Is this necessary?