statistics: entropy plugin - fix placement of entropy.lua

Move the file entropy.lua to the correct directory.

Signed-off-by: Hannu Nyman <redacted>

diff --git a/applications/luci-app-statistics/luasrc/statistics/rrdtool/entropy.lua b/applications/luci-app-statistics/luasrc/statistics/rrdtool/definitions/entropy.lua
similarity index 100%
rename from applications/luci-app-statistics/luasrc/statistics/rrdtool/entropy.lua
rename to applications/luci-app-statistics/luasrc/statistics/rrdtool/definitions/entropy.lua