Merge bitcoin/bitcoin#28714: doc: remove release note fragments for 26.x branch

1ac5584 doc: remove release note fragments for 26.x branch (fanquake)
799ce4d build: bump version to 26.99 (fanquake)

Pull request description:

  26.x has been branched. Delete all release note fragments from this branch.
  Bump master version to 26.99.

ACKs for top commit:
  stickies-v:
    ACK 1ac5584

Tree-SHA512: d7d0c26333ed026460fb648ff5cb8f2f3abe150b47dcf011a563b8fcaad6efe59688f3aa2f23c246e003e37d9b612bb9b9f017ad17cf575455e3f73c6948cff8

Author: fanquake

configure.ac

@@ -1,5 +1,5 @@
 AC_PREREQ([2.69])
-define(_CLIENT_VERSION_MAJOR, 25)
+define(_CLIENT_VERSION_MAJOR, 26)
 define(_CLIENT_VERSION_MINOR, 99)
 define(_CLIENT_VERSION_BUILD, 0)
 define(_CLIENT_VERSION_RC, 0)