Revert "Split off library classes from server/patch/ into diff/"

This reverts commit 0d157b3561.

Reason for revert: full class name goes into H2 keys and values,
and possibly in other data structures in other deployments
(eg. at google), causing cache misses, warnings and/or more
cache dysfunction.

See also https://bugs.chromium.org/p/gerrit/issues/detail?id=7784&desc=2

Change-Id: I03851b8f783b93929e7dc27548fb75882b6bfe05

java/com/google/gerrit/server/BUILD

@@ -38,7 +38,6 @@ java_library(
         "//java/com/google/gerrit/metrics",
         "//java/com/google/gerrit/prettify:server",
         "//java/com/google/gerrit/reviewdb:server",
-        "//java/com/google/gerrit/server/diff",
         "//java/com/google/gerrit/server/ioutil",
         "//java/com/google/gerrit/util/cli",
         "//java/com/google/gerrit/util/ssl",