Stop setting $HOSTNAME in mkshrc.

bash sets this itself. mksh doesn't, but we can set it in adbd instead.

Bug: N/A
Test: `adb shell printenv` and `adb shell`, `printenv`
Change-Id: I3967681c9c6f7bf9b1365f8361e4960e40e4f916

mkshrc

@@ -6,10 +6,8 @@
 #
 # Support: https://launchpad.net/mksh
 
-: ${HOSTNAME:=$(getprop ro.product.device)}
-: ${HOSTNAME:=android}
 : ${TMPDIR:=/data/local/tmp}
-export HOSTNAME TMPDIR
+export TMPDIR
 
 if (( USER_ID )); then PS1='$'; else PS1='#'; fi
 PS4='[$EPOCHREALTIME] '; PS1='${|

mkshrc_vendor

@@ -6,10 +6,6 @@
 #
 # Support: https://launchpad.net/mksh
 
-: ${HOSTNAME:=$(getprop ro.product.device)}
-: ${HOSTNAME:=android}
-export HOSTNAME
-
 if (( USER_ID )); then PS1='$'; else PS1='#'; fi
 PS4='[$EPOCHREALTIME] '; PS1='${|
 	local e=$?