Remove legacy-editable option from setuptools builds (#13059)

We needed this back when `setuptools` first introduced the new editable
installations, but at this point it should work more correctly without
it; our non-CI configurations haven't included it for some time.

(cherry picked from commit 05a9b55)

.azure/test-linux.yml

@@ -92,8 +92,6 @@ jobs:
             # Build and install both qiskit and qiskit-terra so that any optionals
             # depending on `qiskit` will resolve correctly.
           displayName: "Install Terra directly"
-          env:
-            SETUPTOOLS_ENABLE_FEATURES: "legacy-editable"
 
       - ${{ if eq(parameters.installOptionals, true) }}:
         - bash: |
@@ -178,8 +176,6 @@ jobs:
             sudo apt-get install -y graphviz pandoc
             image_tests/bin/pip check
           displayName: 'Install dependencies'
-          env:
-            SETUPTOOLS_ENABLE_FEATURES: "legacy-editable"
 
         - bash: |
             echo "##vso[task.setvariable variable=HAVE_VISUAL_TESTS_RUN;]true"

.azure/test-macos.yml

@@ -48,8 +48,6 @@ jobs:
             # depending on `qiskit` will resolve correctly.
           pip check
         displayName: 'Install dependencies'
-        env:
-          SETUPTOOLS_ENABLE_FEATURES: "legacy-editable"
 
       - ${{ if eq(parameters.installOptionals, true) }}:
         - bash: |

.azure/test-windows.yml

@@ -47,8 +47,6 @@ jobs:
           # depending on `qiskit` will resolve correctly.
           pip check
         displayName: 'Install dependencies'
-        env:
-          SETUPTOOLS_ENABLE_FEATURES: "legacy-editable"
 
       - ${{ if eq(parameters.installOptionals, true) }}:
         - bash: |

.github/workflows/coverage.yml

@@ -47,7 +47,6 @@ jobs:
           CARGO_INCREMENTAL: 0
           RUSTFLAGS: "-Cinstrument-coverage"
           LLVM_PROFILE_FILE: "qiskit-%p-%m.profraw"
-          SETUPTOOLS_ENABLE_FEATURES: "legacy-editable"
 
       - name: Generate unittest coverage report
         run: |

.github/workflows/slow.yml

@@ -21,8 +21,6 @@ jobs:
           python -m pip install -U -r requirements-dev.txt -c constraints.txt
           python -m pip install -c constraints.txt -e .
           python -m pip install "qiskit-aer" "z3-solver" "cplex" -c constraints.txt
-        env:
-          SETUPTOOLS_ENABLE_FEATURES: "legacy-editable"
       - name: Run all tests including slow
         run: stestr run
         env: