serials importer: broken matching by titles

[anikachurilova]

When importing serials, title normalizer is supposed to remove substrings [" series", " ser", " Series", " Ser"] from the end of the title.
Currently, it is removing those substrings from the whole string, resulting in such normalised titles:

• "Springer Series in Statistics Series" --> "springeries in statistics" (expected value is "springer series in statistics")
• "International series of Numerical mathematics ser" --> "internationalies of numerical mathematics" (expected value is "international series of numerical mathematics")

As a result - no matches found by the broken title in the existing serials and the serial with the same title gets imported as a new one.