Bug 1412431 - Remove MOZ_UNIFY_BDATE; r=nalexander

There are no references to this variable outside client.mk. AFAICT
it is unused.

The only reasonable justification for retaining this support IMO was
Universal MacOS builds. And those are no longer supported.

MozReview-Commit-ID: 9MnC18Bd1ge

--HG--
extra : rebase_source : 16c96dfceffb89434489b79f3f4ca2c48506840f

client.mk

@@ -30,8 +30,6 @@
 #   MOZ_PREFLIGHT      }   MOZ_BUILD_PROJECTS, before each project, after
 #   MOZ_POSTFLIGHT     }   each project, and after all projects; these
 #   MOZ_POSTFLIGHT_ALL }   variables contain space-separated lists
-#   MOZ_UNIFY_BDATE      - Set to use the same bdate for each project in
-#                          MOZ_BUILD_PROJECTS
 #
 #######################################################################
 # Defines
@@ -250,18 +248,6 @@ profiledbuild::
 	$(MAKE) -f $(TOPSRCDIR)/client.mk realbuild MOZ_PROFILE_USE=1 CREATE_MOZCONFIG_JSON=
 	$(call BUILDSTATUS,TIER_FINISH pgo_profile_use)
 
-#####################################################
-# Build date unification
-
-ifdef MOZ_UNIFY_BDATE
-ifndef MOZ_BUILD_DATE
-ifdef MOZ_BUILD_PROJECTS
-MOZ_BUILD_DATE = $(shell $(PYTHON) $(TOPSRCDIR)/build/variables.py buildid_header | awk '{print $$3}')
-export MOZ_BUILD_DATE
-endif
-endif
-endif
-
 #####################################################
 # Preflight, before building any project