MIPS: revert "default r6 if vendor is img"

In commit: 9171de358f,
The default output is set to r6 if the vendor is img,
It is ugly and should not be in upstream.

Let's revert it.

bfd/config.bfd

@@ -1537,7 +1537,7 @@ case "${targ_defvec} ${targ_selvecs}" in
 esac
 
 case "${targ}" in
-  mipsisa32r6* | mipsisa64r6* | mips*-img-*)
+  mipsisa32r6* | mipsisa64r6*)
     targ_cflags="$targ_cflags -DMIPS_DEFAULT_R6=1"
     ;;
 esac

gas/configure

@@ -12211,15 +12211,6 @@ _ACEOF
 	    use_e_mips_abi_o32=1
 	    ;;
 	esac
-	# If Vendor is IMG, then MIPSr6 is used
-	case ${target} in
-	  mips*64*-img-*)
-	    mips_cpu=mips64r6
-	    ;;
-	  mips*-img-*)
-	    mips_cpu=mips32r6
-	    ;;
-	esac
 	# Decide whether to generate 32-bit or 64-bit code by default.
 	# Used to resolve -march=from-abi when an embedded ABI is selected.
 	case ${target} in

gas/configure.ac

@@ -380,15 +380,6 @@ changequote([,])dnl
 	    use_e_mips_abi_o32=1
 	    ;;
 	esac
-	# If Vendor is IMG, then MIPSr6 is used
-	case ${target} in
-	  mips*64*-img-*)
-	    mips_cpu=mips64r6
-	    ;;
-	  mips*-img-*)
-	    mips_cpu=mips32r6
-	    ;;
-	esac
 	# Decide whether to generate 32-bit or 64-bit code by default.
 	# Used to resolve -march=from-abi when an embedded ABI is selected.
 	case ${target} in