Remove broken-smt-backend tag from passing tests

These pass at present. No attempt to bisect and link to the respective fixes has
been made.

Author: tautschnig

regression/cbmc/Anonymous_Struct3/test.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 main.c
 
 ^EXIT=0$

regression/cbmc/Float13/test.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 main.c
 
 ^EXIT=0$

regression/cbmc/Promotion3/test.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 main.c
 
 ^EXIT=0$

regression/cbmc/Quantifiers-assertion/test.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 main.c
 
 ^\*\* Results:$

regression/cbmc/Union_Initialization1/test.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 main.c
 
 ^EXIT=0$

regression/cbmc/array-tests/test.desc

@@ -6,3 +6,5 @@ main.c
 ^VERIFICATION SUCCESSFUL$
 --
 ^warning: ignoring
+--
+This test actually passes with the SMT2 back-end, but takes 88 seconds to do so.

regression/cbmc/graphml_witness1/test.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 main.c
 --graphml-witness -
 ^EXIT=10$

regression/cbmc/union6/test.desc

@@ -1,4 +1,4 @@
-CORE broken-smt-backend
+CORE
 main.c
 --little-endian
 ^EXIT=0$

regression/cbmc/variable-access-to-constant-array/test.desc

@@ -6,3 +6,5 @@ main.c
 ^VERIFICATION FAILED$
 --
 ^warning: ignoring
+This test actually passes when using the SMT2 back-end, but takes 68 seconds to
+do so.