Spin dynamics in zincblende two-dimensional electron systems is usually dominated by the Dyakonov-Perel spin dephasing mechanism resulting from the underlying spin-orbit fields. An exceptional situation is realized in symmetrically grown and doped GaAs/AlGaAs quantum wells grown along the [110] direction, where the Rashba contribution is negligible and the effective Dresselhaus spin-orbit field is perpendicular to the sample plane. In such a system the spin dephasing times for in- and out-of-plane crystallographic directions are expected to be strongly different and the out-of-plane spin dephasing time is significantly enhanced as compared with conventional systems. We observe the spin relaxation anisotropy by resonant spin amplification measurements in a 30 nm wide double-sided symmetrically δ-doped single quantum well with a very high mobility of about 3·10⁶ cm ²/Vs at 1.5K. A comparison of the measured resonant spin amplification traces with the developed theory taking into account the spin dephasing anisotropy yields the dephasing times whose anisotropy and magnitudes are in-line with the theoretical expectations.