Remove makefile logic for legacy -this-package-key

This isn't needed anymore as we don't support GHC < 8 anymore.

This is a follow-up to 122f183d

configure.ac

@@ -176,11 +176,6 @@ fi
 GHC_PACKAGE_DB_FLAG=package-db
 AC_SUBST(GHC_PACKAGE_DB_FLAG)
 
-FP_COMPARE_VERSIONS([$GhcVersion],[-lt],[7.11],
-                    SUPPORTS_THIS_UNIT_ID=NO,
-                    SUPPORTS_THIS_UNIT_ID=YES)
-AC_SUBST(SUPPORTS_THIS_UNIT_ID)
-
 # GHC is passed to Cabal, so we need a native path
 if test "${WithGhc}" != ""
 then

mk/config.mk.in

@@ -510,8 +510,6 @@ endif
 
 GHC_PACKAGE_DB_FLAG = @GHC_PACKAGE_DB_FLAG@
 
-SUPPORTS_THIS_UNIT_ID = @SUPPORTS_THIS_UNIT_ID@
-
 #-----------------------------------------------------------------------------
 # C compiler
 #

rules/distdir-way-opts.mk

@@ -105,20 +105,10 @@ define distdir-way-opts # args: $1 = dir, $2 = distdir, $3 = way, $4 = stage
 # $1_$2_$3_MOST_HC_OPTS is also passed to C compilations when we use
 # GHC as the C compiler.
 
-ifeq "$(SUPPORTS_THIS_UNIT_ID)" "NO"
-ifeq "$4" "0"
-$4_USE_THIS_UNIT_ID=NO
-endif
-endif
-
 $1_$2_$4_DEP_OPTS = \
  $$(foreach pkg,$$($1_$2_DEP_IPIDS),-package-id $$(pkg))
 
-ifeq "$($4_USE_THIS_UNIT_ID)" "NO"
-$4_THIS_UNIT_ID = -this-package-key
-else
 $4_THIS_UNIT_ID = -this-unit-id
-endif
 
 $1_$2_$3_MOST_HC_OPTS = \
  $$(WAY_$3_HC_OPTS) \