Makefile: clean .depend dirs under COMPUTE_HEADER_DEPENDENCIES != yes

Fix a logic error in dfea575 (Makefile: lazily compute header
dependencies, 2010-01-26) where we'd make whether we cleaned the
.depend dirs contingent on the currently configured
COMPUTE_HEADER_DEPENDENCIES value. Before this running e.g.:

    make COMPUTE_HEADER_DEPENDENCIES=yes grep.o
    make COMPUTE_HEADER_DEPENDENCIES=no clean

Would leave behind the .depend directory, now it'll be removed.

Normally we'd need to use another variable, but in this case there's
no other uses of $(dep_dirs), as opposed to $(dep_args) which is used
as an argument to $(CC). So just deleting this line makes everything
work correctly.

See http://lore.kernel.org/git/[email protected] for a report
about this issue.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

Makefile

@@ -2477,7 +2477,6 @@ dep_args = -MF $(dep_file) -MQ $@ -MMD -MP
 endif
 
 ifneq ($(COMPUTE_HEADER_DEPENDENCIES),yes)
-dep_dirs =
 missing_dep_dirs =
 dep_args =
 endif