build: fix dependency issues with man page generation

build: fix dependency issues with man page generation

* .gitignore: Remove reference to no longer generated make file.
* configure.ac: Don't bother generating placeholder make file.
* man/local.mk: Hardcode the man page deps list for normal builds
to be compatible with all make implementations and configure options.
Note in SINGLE_BINARY mode, all man pages will be generated on
any change to the coreutils binary, but development will generally
not be done in this mode, so this shouldn't be an issue.

Fixes http://bugs.gnu.org/18055