removing non-existing file from the build

Summary: broken by D2096146

Test Plan: arc unit

Reviewed By: andrewcox@fb.com

Subscribers: folly-diffs@, yfeldblum, chalfant

FB internal diff: D2100773

Signature: t1:2100773:1432676073:a72e72fa5fb915b027fdfd31dd814d02e6606858

folly/Makefile.am

@@ -374,7 +374,6 @@ libfolly_la_SOURCES = \
 	io/async/EventBase.cpp \
 	io/async/EventBaseManager.cpp \
 	io/async/EventHandler.cpp \
-	io/async/Request.cpp \
 	io/async/SSLContext.cpp \
 	io/async/HHWheelTimer.cpp \
 	io/async/test/TimeUtil.cpp \