Revert "Specify python3 version in apt install commands"

This reverts commit 1925e87ad52dcca103cd507185bf2aea48817124.

Reason for revert: gLinux is now on 3.10 and debian:testing no longer supports 3.9

Change-Id: I7ccabf16a8951b05dd98b3010d0ca068239e97e8

install-prereqs.sh

diff --git a/install-prereqs.sh b/install-prereqs.sh
index 99986d4..d44c388 100755
--- a/install-prereqs.sh
+++ b/install-prereqs.sh
@@ -75,8 +75,8 @@
     pv
     python-is-python3
     python3-protobuf
-    python3.9
-    python3.9-dev
+    python3
+    python3-dev
     python3-pip
     rsync
     srecord