cputest: remove stibp flag from test data

stibp flag doesn't exist in this maint branch.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

tests/cputestdata/x86_64-cpuid-Xeon-E3-1225-v5-guest.xml

@@ -20,7 +20,6 @@
   <feature policy='require' name='tsc_adjust'/>
   <feature policy='require' name='clflushopt'/>
   <feature policy='require' name='md-clear'/>
-  <feature policy='require' name='stibp'/>
   <feature policy='require' name='ssbd'/>
   <feature policy='require' name='xsaves'/>
   <feature policy='require' name='pdpe1gb'/>

tests/cputestdata/x86_64-cpuid-Xeon-E3-1225-v5-host.xml

@@ -21,7 +21,6 @@
   <feature name='tsc_adjust'/>
   <feature name='clflushopt'/>
   <feature name='md-clear'/>
-  <feature name='stibp'/>
   <feature name='ssbd'/>
   <feature name='xsaves'/>
   <feature name='pdpe1gb'/>

tests/cputestdata/x86_64-cpuid-Xeon-E3-1225-v5-json.xml

@@ -6,7 +6,6 @@
   <feature policy='require' name='tsc_adjust'/>
   <feature policy='require' name='clflushopt'/>
   <feature policy='require' name='md-clear'/>
-  <feature policy='require' name='stibp'/>
   <feature policy='require' name='ssbd'/>
   <feature policy='require' name='pdpe1gb'/>
 </cpu>