[SPARK-6103][Graphx]remove unused class to import in EdgeRDDImpl

[lianhuiwang]

Class TaskContext is unused in EdgeRDDImpl, so we need to remove it from import list.

[SparkQA]

Test build #28154 has started for PR 4846 at commit 31aed64.

• This patch merges cleanly.

[SparkQA]

Test build #28154 has finished for PR 4846 at commit 31aed64.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • class MatrixFactorizationModel(JavaModelWrapper, Saveable, JavaLoader):
  • class Saveable(object):
  • class Loader(object):
  • class JavaLoader(Loader):
  • java_class = ".".join([java_package, cls.__name__])

[AmplabJenkins]

Test PASSed.
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https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/28154/
Test PASSed.

[srowen]

I don't mean to pick on this, but it's an example: this is a trivial, nonfunctional change. Opening a JIRA, opening a PR, emailing the list twice, asking for review, getting it merged, takes up probably a whole hour of time across the various people involved. There is also a very tiny chance that it causes a merge conflict later which has to be manually resolved.

We are still well over 100% capacity to review and merge changes too, so I want to start pushing back a little on things like this.

I do not think it is worth opening issues this small. Instead consider touching up small issues like this when nearby code is already changing. That said, this seems uncontroversial to merge.