eal: fix duplicate function declaration

eal: fix duplicate function declaration

The rte_eal_get_runtime_dir() function is currently being declared in two
header files.

This API was made public in commit 6911c9fd8fbe ("eal: export function to
get runtime directory"), adding it to rte_eal.h. To make it public, the
'rte' prefix was added to the function so it needed to be modified in the
original location of the declaration, eal_filesystem.h.  By only modifying,
and not removing the decalration, it is now a duplicate.

This patch removes the declaration from eal_filesystem.h.

Fixes: 6911c9fd8fbe ("eal: export function to get runtime directory")

Reported-by: Anatoly Burakov <anatoly.burakov@intel.com>
Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>