The @= in `spack find` output adds a bit of noise. Remove it as we
did for `spack spec` and `spack concretize`.
This modifies display_specs so it actually covers other places we use that routine, as
well, e.g., `spack buildcache list`.
before:
```
-- linux-ubuntu20.04-aarch64 / gcc@=11.1.0 -----------------------
ofdlcpi libpressio@0.88.0
```
after:
```
-- linux-ubuntu20.04-aarch64 / gcc@11.1.0 -----------------------
ofdlcpi libpressio@0.88.0
```
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