Unwanted execution of ImmutableEnumChecker by enabling Immutable check

Hi,

there is most likely some mistake in how these two checks are configured leading to false activation of unintended checks:

**Immutable**

* Type declaration annotated with `@Immutable` is not immutable
* https://errorprone.info/bugpattern/Immutable
* Severity: ERROR by default

**ImmutableEnumChecker**

* Enums should always be immutable
* https://errorprone.info/bugpattern/ImmutableEnumChecker
* Severity: WARNING by default
* ⚠ Alternate names: **Immutable**

The `ImmutableEnumChecker` warning declares the same name as the `Immutable` error.

Given a code that has `-XepDisableAllChecks -XepDisableAllWarnings -Xep:Immutable:ERROR`, trying to enable the former `Immutable` error for checking the `@Immutable` annotated types, it mistakenly activates the `ImmutableEnumChecker` at an ERROR level leading to unwanted failures.