mail/fetchmail: update to 6.4.24 and block LibreSSL.

fetchmail cannot legally be linked with LibreSSL,
because there is no GPLv2 clause 2b exemption for
LibreSSL, only for OpenSSL.

Correct LICENSE and remove LICENSE_COMB.
Add comment on FSF dynamic linking dynamically
suggested by Corey Halpin in the approval.

Remove LibreSSL patch.

Related to:
PR: 259214

Update:
PR: 259945
MFH: 2021Q4

Approved by: chalpin@cs.wisc.edu (maintainer)

(cherry picked from commit 997bacb528ceba53b9e680dff833a0258d3bf917)