gh-36965: Update system package info for slackware
    
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URL: #36965
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee

Author: Release Manager

build/pkgs/_prereq/distros/slackware.txt

@@ -13,19 +13,16 @@ make
 guile
 gc
 libffi
-gcc-[0-9]      # So that slackpkg pattern matching does not pull in all gcc-* packages
-gcc-11           # on slackware-current
-gcc-g++
-gcc-g++-11       # on slackware-current
+gcc-13
+gcc-g++-13
 # dependencies of gcc
 libmpc
 glibc
 kernel-headers
 perl
 m4
 bc
-python-2.7       # on slackware-14.2
-python3          # on slackware-current
+python3
 flex
 # for https upstream_url downloads
 ca-certificates