The SPEC file does not reflect the actual dependencies of current versions of Calibre. Some of them can be dropped to reduce the footprint of the installation.

Dependencies to be removed:
Requires: python-cherrypy -> not required since 3.0 [1]
Requires: python-genshi -> not required since 0.9.33 [2]
Requires: python-cssselect -> not required since 2.21.0 [3]

Calibre no longer ships embedded copies of cherrypy [1], cssutils [4], encutils (which is now part of cssutils) and trac. The following lines should therefore be removed (except for odf, which is still included and can be replaced by the external python2-odfpy package).
rm -rf %{buildroot}%{_libdir}/%{name}/{odf,cherrypy,encutils,cssutils}
rm -rf %{buildroot}%{_libdir}/%{name}/cal/utils/genshi
rm -rf %{buildroot}%{_libdir}/%{name}/cal/trac

I also noticed that the following line has no effect (the respective files do not include any \r\n style newlines) and should be removed as well.
sed -i 's/\r//' src/calibre/web/feeds/recipes/*

Judging from the official list of external applications used by Calibre [5], it might also be required to add some new packages to the SPEC file. But up to now I did not come across any errors because of missing dependencies.

[1] https://github.com/kovidgoyal/calibre/commit/5ed88a0bf596ea4389ac4fe08ccf249c7693d04d
[2] https://github.com/kovidgoyal/calibre/commit/276ec769f7d863ef5bd413387d9ea8312434e2db
[3] https://github.com/kovidgoyal/calibre/commit/97b8daee41ce47c385000003075107fb4f16fe3a
[4] https://github.com/kovidgoyal/calibre/commit/d4afa232cd93dc33f7d24712aa4f2dc7165bef72
[5] https://github.com/kovidgoyal/build-calibre/blob/master/scripts/sources.json