Remove fee handler and fix post-handler error handling.

[SpicyLemon]

Description

This PR makes a couple changes needed for the flat-fees stuff:

• Remove the fee handler. The SDK now has a post handler which is essentially the same thing we had added with our fee handler customization. So we remove our customization and switch to using what the SDK now provides.
• Improves error handling when the post handler returns an error. The SDK fixed this with fix(baseapp): Fix post handler error always results in code 1 cosmos/cosmos-sdk#24261 but didn't backport it.

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[SpicyLemon]

I ran the following make targets locally and they all completed successfully:

• make test
• make test-sim-nondeterminism
• make test-sim-import-export
• make test-sim-after-import
• make test-sim-multi-seed-short

The tests in the orm dir fail to compile because the SDK ripped out a bunch of stuff (but not all of it). But we don't use any of the orm stuff, and it's in its own library/package so that's fine.