Remove folded-in changes files

changes/bug26272

-  o Minor bugfixes (compilation):
-    - Silence unused-const-variable warnings in zstd.h on some gcc versions.
-      Fixes bug 26272; bugfix on 0.3.1.1-alpha.

changes/bug26283

-  o Minor bugfixes (C correctness):
-    - Avoid casting return value of smartlist_len() to double as
-      compiler does not like it when -Wbad-function-cast is on.
-      Fixes bug 26283; bugfix on 0.2.4.10-alpha.

changes/geoip-2018-06-07

-  o Minor features (geoip):
-    - Update geoip and geoip6 to the June 7 2018 Maxmind GeoLite2
-      Country database. Closes ticket 26351.
-