Do not print parentheses if not needed

Currently the formatter puts parentheses around expressions even if they are not needed:

$ lfortran fmt integration_tests/program_01.f90 
program program_01
integer, parameter :: dp=kind(0.d0)
real :: a
integer :: i
print *, "Normal random numbers:"
do i = 1, 10
    call rand(a)
    print *, a
end do

contains

    subroutine rand(x)
    real, intent(out) :: x
    logical, save :: first=.true.
    real, save :: u(2)
    real :: r2
    if (first) then
        do
            call random_number(u)
            u = ((2)*(u)) - (1)
            r2 = sum((u)**(2))
            if (((r2)<(1)).and.((r2)>(0))) then
                exit
            end if
        end do
        u = (u)*(sqrt(((-(2))*(log(r2)))/(r2)))
        x = u(1)
    else
        x = u(2)
    end if
    first = .not.(first)
    end subroutine rand

end program program_01

We should use Fortran semantics to only put parentheses when they are needed.