remove old link to header selinux/flask.h and selinux/av_permissions.h and depend...

remove old link to header selinux/flask.h and selinux/av_permissions.h and depend (#12)

* 1. remove link to header selinux/flask.h and selinux/av_permissions.h
2. simple move from constant's SECCLASS_FILE and FILE__ENTRYPOINT to functions string_to_security_class("file") and string_to_av_perm(tclass, "entrypoint")
3. NEED CHECK CORRECT RETURN AFTER FAILED RETURN FROM FUNCTION string_to_security_class ADN string_to_av_perm !
Link to info from libselinux
https://github.com/SELinuxProject/selinux/commit/76913d8adb61b5#diff-046564229793ada24798dac3d2e479f07651ac9020d43938f3aa1fa9c9c24c9e

* read_conf() selinux: renamed vars and added error return

Co-authored-by: Thibault Godouet <yo8192@users.noreply.github.com>