Merge bitcoin#25521: build: Remove outdated libbitcoinkernel comment

18f5355 Remove outdated comment (Igor Bubelov)

Pull request description:

  Looks like this comment is no longer relevant, the last files which matched `index/*.cpp` pattern were removed in bitcoin@f100687

ACKs for top commit:
  dongcarl:
    ACK 18f5355
  shaavan:
    ACK 18f5355

Tree-SHA512: d3fcc2db0940f81ce521fddff836f271709ea327c357942383f8aff6c7089e74490fa720e7a2916900215c733d2b64960c1aa185f0c9b1567fce90a249d405e0

Author: MacroFake

src/Makefile.am

@@ -854,8 +854,7 @@ endif
 
 # TODO: libbitcoinkernel is a work in progress consensus engine library, as more
 #       and more modules are decoupled from the consensus engine, this list will
-#       shrink to only those which are absolutely necessary. For example, things
-#       like index/*.cpp will be removed.
+#       shrink to only those which are absolutely necessary.
 libbitcoinkernel_la_SOURCES = \
   kernel/bitcoinkernel.cpp \
   arith_uint256.cpp \