remove deprecated HexGrid class

[quaquel]

This removes the long deprecated HexGrid class from mesa.space.

closes #1847

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
BoltzmannWealth	small	🔴 +7.2% [+5.6%, +8.8%]	🔵 +0.3% [+0.2%, +0.5%]
BoltzmannWealth	large	🔵 -1.1% [-1.6%, -0.7%]	🔵 +2.0% [+0.7%, +3.2%]
Schelling	small	🔵 +0.7% [+0.3%, +1.2%]	🔵 -0.4% [-0.8%, -0.1%]
Schelling	large	🔵 +0.4% [-0.6%, +1.2%]	🔵 +1.0% [-1.7%, +3.6%]
WolfSheep	small	🔵 -1.0% [-1.2%, -0.8%]	🔵 +0.1% [-0.1%, +0.4%]
WolfSheep	large	🔵 -1.9% [-3.3%, -0.5%]	🔵 -1.4% [-4.4%, +1.5%]
BoidFlockers	small	🔵 -0.9% [-1.4%, -0.4%]	🔵 -0.6% [-1.5%, +0.3%]
BoidFlockers	large	🔵 -0.1% [-0.7%, +0.5%]	🔵 +0.3% [-0.2%, +1.0%]

[EwoutH]

Looks good. Are there tests that can/need to be removed?

[quaquel]

Looks good. Are there tests that can/need to be removed?

those would have broken and all tests pass, so no.