Back out "Update folly's source of truth to xplat"

Summary: Original commit changeset: 6362acb7a668 (D23066827 (https://github.com/facebook/folly/commit/0b3d9d21b7d1496e0b592ee6ce7a687c86c0498f))

Reviewed By: yfeldblum

Differential Revision: D23837145

fbshipit-source-id: 642c1401aea0b01c0c5e53c24b100f5daa600512

build/fbcode_builder/manifests/folly

 [manifest]
 name = folly
-fbsource_path = xplat/folly
+fbsource_path = fbcode/folly
 shipit_project = folly
 shipit_fbcode_builder = true
 
@@ -41,12 +41,12 @@ openssl
 zlib
 
 [shipit.pathmap]
-xplat/folly/public_tld = .
-xplat/folly = folly
+fbcode/folly/public_tld = .
+fbcode/folly = folly
 
 [shipit.strip]
-^xplat/folly/folly-config\.h$
-^xplat/folly/public_tld/build/facebook_.*
+^fbcode/folly/folly-config\.h$
+^fbcode/folly/public_tld/build/facebook_.*
 
 [cmake.defines]
 BUILD_SHARED_LIBS=OFF