Adjust .pc file not to expose used crypto library

Public headers of Evolution Data Server (and Camel) are not directly including headers of the crypto library NSS. The shared libraries already have links so NSS is at best only needed for static linking, but that must go into a the field called private. The same applies for SQLite in Camel.

Caused by commit 7330f2e1 and 355986b9. The same issue was found in libSRTP. Then, on recent Ubuntu (21.10), similar packages were searched via $ apt-cache rdepends libnspr4-dev. The packages libcamel1.2-dev and evolution-data-server-dev appeared (two of three). Then, the latest source and the headers were checked whether they include headers of NSS (and here SQLite).

Commit 1c79f8a6 introduced @MANUAL_NSS_LIBS@. Because that is legacy stuff not showing up in the final .pc file on Debian/Ubuntu at all, I did not touch it.