  We report the evolution of the electronic nematic susceptibility in FeSe via
Raman scattering as a function of hydrostatic pressure up to 5.8 GPa where the
superconducting transition temperature $T_{c}$ reaches its maximum. The
critical nematic fluctuations observed at low pressure vanish above 1.6 GPa,
indicating they play a marginal role in the four-fold enhancement of $T_{c}$ at
higher pressures. The collapse of nematic fluctuations appears to be linked to
a suppression of low energy electronic excitations which manifests itself by
optical phonon anomalies at around 2 GPa, in agreement with lattice dynamical
and electronic structure calculations using local density approximation
combined with dynamical mean field theory. Our results reveal two different
regimes of nematicity in the phase diagram of FeSe under pressure: a d-wave
Pomeranchuk instability of the Fermi surface at low pressure and a magnetic
driven orthorhombic distortion at higher pressure.
