cuproj: remove pin on 'proj' in conda packages (#1449)

Proposes removing the `cuproj` conda package's pin on `proj`, so that it can build using the same version that `conda-forge` pins to in https://github.com/conda-forge/conda-forge-pinning-feedstock.

For context, see:

* why the `proj==9.3.0` pin was originally added: #1307
* `conda-forge` completied migrations:
  - `9.3.1`: conda-forge/conda-forge-pinning-feedstock#5401
  - `9.4.`: conda-forge/conda-forge-pinning-feedstock#6240

Authors:
  - James Lamb (https://github.com/jameslamb)

Approvers:
  - https://github.com/jakirkham

URL: #1449

conda/recipes/cuproj/conda_build_config.yaml

@@ -18,7 +18,3 @@ c_stdlib_version:
 
 cmake_version:
   - ">=3.26.4,!=3.30.0"
-
-# Workaround until proj 9.3.1 migration completes
-proj:
-  - "9.3.0"