Bazel: Change deprecated single file attribute parameter
Bazel: Change deprecated single file attribute parameter

single_file attribute is deprecated: [1] and should be replaced with
allow_single_file.

[1] https://docs.bazel.build/versions/master/skylark/lib/attr.html#parameters-3

Change-Id: I72f955ac47764c4eeb1ad65ab1f4b27db590521f

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