Revert parallel query NULL checks that caused CI timeout

The NULL checks for exec_state_call_stack added in commits 99d9d2f
and 31c1136 were causing general JDBC tests to timeout. These checks
were intended to fix parallel query crashes but inadvertently broke
the normal execution path.

This reverts those specific changes while keeping the important fixes:
- 1c80f61: Fix INSERT EXEC snapshot error with AFTER triggers
- df12e05: Fix INSERT EXEC INSTEAD OF triggers on view targets
- 7d020a7: Fix C90 failure

Parallel query tests may still fail (separate issue), but general
JDBC tests should now pass without timeout.

Author: monk0707

contrib/babelfishpg_tsql/src/iterative_exec.c

@@ -951,10 +951,6 @@ is_part_of_pltsql_trycatch_block(PLtsql_execstate *estate)
 	PLExecStateCallStack *cur;
 	int level = 0;
 
-	/* Safety check for parallel workers where exec_state_call_stack may be NULL */
-	if (exec_state_call_stack == NULL)
-		return false;
-
 	Assert(estate == exec_state_call_stack->estate);
 	cur = exec_state_call_stack;
 	while (cur != NULL)
@@ -992,10 +988,6 @@ is_part_of_pltsql_trigger(PLtsql_execstate *estate)
 {
 	PLExecStateCallStack *cur;
 
-	/* Safety check for parallel workers where exec_state_call_stack may be NULL */
-	if (exec_state_call_stack == NULL)
-		return false;
-
 	Assert(estate == exec_state_call_stack->estate);
 	cur = exec_state_call_stack;
 	while (cur != NULL)