can't tickquote combinee objects if finalize_funs=FALSE

In #127 I added `tickquote_combinee_objects` argument to `create_task_makefile()`. There I said I intended to deprecate and ultimately remove that argument to make it effectively always TRUE.

But that's a bad idea (to remove that arg) currently, because if finalize_funs=FALSE and the final targets are R objects, then tickquoting them currently causes the default target to depend on a list of tickquoted objects...but then `yaml::yaml.load_file` (called from `scmake()`) will throw an error because you're not allowed to tickquote yaml entries.

One solution would be to keep the arg around. Another better one would be to not tickquote the entries in the `depends` list of the default target.

Read create_task_makefile() and scmake(), then trace how the default target's depends entries are serialized and loaded through yaml::yaml.load_file when finalize_funs=FALSE. Done means final R-object targets no longer cause a yaml tickquote error while their dependencies remain correct.

Written by the indexing model from the issue text.