/usr/share/postgresql/9.4/extension/postgis--2.1.4--2.1.4next.sql is in postgresql-9.4-postgis-scripts 2.1.4+dfsg-3.
This file is owned by root:root, with mode 0o644.
It is a symlink to /usr/share/postgresql/9.4/extension/./usr/share/postgresql/9.4/extension/postgis--2.1.0rc1--2.1.4.sql