exec: Remove env from list of poisoned names

The global variable env was removed some time ago, so this name may be
used without any restriction now.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

include/exec/poison.h

@@ -36,7 +36,6 @@
 #pragma GCC poison TARGET_PAGE_ALIGN
 
 #pragma GCC poison CPUArchState
-#pragma GCC poison env
 
 #pragma GCC poison lduw_phys
 #pragma GCC poison ldl_phys