Internal usage of guava and caffeine Cache seems inconsistent

[XN137]

In e1acde9 caffeine was added to the build:

This adds a new dependency on Caffeine; I considered using a Guava
Cache since we already depend on Guava, but Caffeine's version is 3
times as fast for this use case.

however on master a guava cache is also used in a few places:

error-prone/check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/inference/NullnessQualifierInference.java

Lines 22 to 24 in 1c3c09f

	import com.google.common.cache.CacheBuilder;
	import com.google.common.cache.CacheLoader;
	import com.google.common.cache.LoadingCache;

error-prone/check_api/src/main/java/com/google/errorprone/dataflow/DataFlow.java

Lines 21 to 23 in 1c3c09f

	import com.google.common.cache.CacheBuilder;
	import com.google.common.cache.CacheLoader;
	import com.google.common.cache.LoadingCache;

so i was wondering:
is this intentional or would there be value in unifying this?

• using caffeine could (allegedly) give a performance boost
• dropping caffeine would remove the extra dependency

[cushon]

We are slowly moving towards caffeine, PRs to migrate those usages of common.cache are welcome

[Sineaggi]

@cushon I've god a pr that should fix existing usages of common.cache here #3796