pc: clean up COMPAT macro chaining

Since commit
 bacc344c ("machine: add properties to compat_props incrementaly")
there is no need to chain per machine type compat macro.

Clean up places where it was done anyway so it will be
consistent and won't confuse contributors during addtion
of new machine types.
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>

include/hw/i386/pc.h

@@ -375,7 +375,6 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
 
 #define PC_COMPAT_2_7 \
-    PC_COMPAT_2_8 \
     HW_COMPAT_2_7
 
 #define PC_COMPAT_2_6 \
@@ -405,7 +404,6 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
     },
 
 #define PC_COMPAT_2_5 \
-    PC_COMPAT_2_6 \
     HW_COMPAT_2_5
 
 /* Helper for setting model-id for CPU models that changed model-id