Simplified val_type_of_expr using vector_of_val_type and element_val_type 
Simplified val_type_of_expr using vector_of_val_type and element_val_type 

Former-commit-id: 6e3644dff7df94d10d0908658b63c27653edac9e
Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide