test_cbfs: fix to support cbfstool v4.9. Drop < v4.7

v4.8 or v4.9 added a new header " FMAP REGION: COREBOOT", see new contextual diff below. Rather than adding yet another .diff file, add a tiny bit of "fuzziness" thanks to .endswidth() and re-use the v4.7 .diff after removing its inflexible @@ -1,3 +1,3 @@ block header. Keeping one line of context will catch any actual diff change.

Drop all but one .diff file and support for versions < v4.7.

--- coreboot1
+++ ./coreboot2.rom
├── cbfstool {} print
│ @@ -1,4 +1,4 @@
│  FMAP REGION: COREBOOT
│  Name                           Offset     Type           Size   Comp
│ -text                           0x0        raw               446 none
│ -(empty)                        0x200      null            32152 none
│ +text                           0x0        raw               671 none
│ +(empty)                        0x300      null            31896 none