follectd: fix indentations and rename folder in libexec

Remove PKG_BUILD_DIR as we dont need to override it Upstream decided not to use variable PKG_NAME in description and so on as it was kinda confusing for them. Details: https://github.com/openwrt/packages/commit/f82287cf5c1b2acd46feb52fb9b3cb3697e7086b

(Fixes: 47524d1e - follectd: name fixes 'follect' -> 'follectd') Due to: install: cannot create regular file '/****/build/build_dir/target-aarch64_cortex-a53_musl/follectd/.pkgdir/follectd/usr/libexec/follectd/neighbours.sh': No such file or directory

cc: @shenek

WIP state: I'm still building it locally, it should pass within a few minutes.