[split] util-core: delete an unused line in a test

RB_ID=346953
[split] finagle-mux: GC Avoidance primitives Problem GC Avoidance is a tricky problem, and requires a small set of tools so we can talk about it in sophisticated ways.

Result
We have a simple toolkit to build GC Avoidance on top of.

RB_ID=343361
[split] util-app: Add flag for configuring acceptance of undefined flags

The default behaviour of App with respect to undefined flags (allowing
them) is rather surprising given that most flag parsing libraries will
barf if passed a flag they don't know about. This change leaves the
default behaviour intact, but allows undefined flags to be disallowed
through the `allowUndefinedFlags` method.

Signed-off-by: Evan Meagher <evm@twitter.com>

RB_ID=347823
TBR=true
[split] finagle/util: Minor c.t.app.ClassPath/c.t.f.util.LoadService cleanup

Fix a couple rough edges in com.twitter.app.ClassPath
and com.twitter.finagle.util.LoadService:

- LoadService doesn't use either of the name vals defined within Info.
- ClassPath uses `name`, but unconditionally chops off the last six
  characters of path strings rather than only doing so for .class files.

RB_ID=354443
[split] util-core: Moves Sleeper => Time.sleep Problem Testing sleeping is tricky.  The first implementation made the scaffolding nice, but sacrificed the API.  This was the wrong tradeoff.

Result
Sleeper => Time.sleep

This is only used for testing.  It should simplify the language around testing for nearly all common cases, although some edge cases will not be served as well.

For no extra work, if you use Time.sleep, it will track with the TimeControl from your Time.withCurrentTimeFrozen.

RB_ID=352941
[split] util-app: Rm extraneous println prior to flag-parsing

RB_ID=356127
[split] bump util to 6.16.1-SNAPSHOT

RB_ID=357283
TBR=true