[SPARK-5254][MLLIB] remove developers section from spark.ml guide

Forgot to remove this section in #4052.

Author: Xiangrui Meng <meng@databricks.com>

Closes #4053 from mengxr/SPARK-5254-update and squashes the following commits:

f295bde [Xiangrui Meng] remove developers section from spark.ml guide

docs/ml-guide.md

@@ -689,17 +689,3 @@ Spark ML currently depends on MLlib and has the same dependencies.
 Please see the [MLlib Dependencies guide](mllib-guide.html#Dependencies) for more info.
 
 Spark ML also depends upon Spark SQL, but the relevant parts of Spark SQL do not bring additional dependencies.
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-# Developers
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-**Development plan**
-
-If all goes well, `spark.ml` will become the primary ML package at the time of the Spark 1.3 release.  Initially, simple wrappers will be used to port algorithms to `spark.ml`, but eventually, code will be moved to `spark.ml` and `spark.mllib` will be deprecated.
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-**Advice to developers**
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-During the next development cycle, new algorithms should be contributed to `spark.mllib`, but we welcome patches sent to either package.  If an algorithm is best expressed using the new API (e.g., feature transformers), we may ask for developers to use the new `spark.ml` API.
-Wrappers for old and new algorithms can be contributed to `spark.ml`.
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-Users will be able to use algorithms from either of the two packages.  The main difficulty will be the differences in APIs between the two packages.
-