cache.py: remove the duplicated self.file_depends

cache.py: remove the duplicated self.file_depends

There are two "self.file_depends =" lines in cache.py::CoreRecipeInfo:

class CoreRecipeInfo(RecipeInfoCommon):
    __slots__ = ()

    cachefile = "bb_cache.dat"

    def __init__(self, filename, metadata):
        self.file_depends = metadata.getVar('__depends', False)
    [snip]
        self.file_depends = metadata.getVar('__depends', False)

They are duplicated, remove the last one.

[YOCTO #3795]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>