Remove PIP_DISABLE_PIP_VERSION_CHECK from workflow environment

Based on the `cibuildwheel` docs, this environment variable is
already defined by `cibuildwheel`:

    https://cibuildwheel.pypa.io/en/stable/options/#environment

Author: molinav

.github/workflows/build.yml

@@ -65,7 +65,6 @@ jobs:
             environment: >-
               GEOS_DIR="/project/packages/basemap/extern"
               LD_LIBRARY_PATH="/project/packages/basemap/extern/lib"
-              PIP_DISABLE_PIP_VERSION_CHECK=1
               PIP_PREFER_BINARY=1
               PYTHONUNBUFFERED=1
               PYTHONWARNINGS="ignore:DEPRECATION"
@@ -82,7 +81,6 @@ jobs:
               "
             environment: >-
               GEOS_DIR="D:/a/basemap/basemap/packages/basemap/extern"
-              PIP_DISABLE_PIP_VERSION_CHECK=1
               PIP_PREFER_BINARY=1
               PYTHONUNBUFFERED=1
               PYTHONWARNINGS="ignore:DEPRECATION"