don't double-install executorch for one-off linux pull-time jobs (#8142)

I remember somebody mentioning they wanted install_executorch to be the one solution previously. CI is red for these jobs due to timeouts and we should not block a time improvement just because it is not the ideal long-term solution.

Author: swolchok

.github/workflows/pull.yml

@@ -220,9 +220,6 @@ jobs:
 
         PYTHON_EXECUTABLE=python bash .ci/scripts/setup-linux.sh "cmake"
 
-        # install pybind
-        bash install_executorch.sh --pybind xnnpack --use-pt-pinned-commit
-
         # install Llava requirements
         bash examples/models/llama/install_requirements.sh
         bash examples/models/llava/install_requirements.sh
@@ -483,9 +480,6 @@ jobs:
 
         PYTHON_EXECUTABLE=python bash .ci/scripts/setup-linux.sh "cmake"
 
-        # install pybind
-        bash install_executorch.sh --pybind xnnpack --use-pt-pinned-commit
-
         # install phi-3-mini requirements
         bash examples/models/phi-3-mini/install_requirements.sh
 
@@ -513,9 +507,6 @@ jobs:
 
         PYTHON_EXECUTABLE=python bash .ci/scripts/setup-linux.sh "cmake"
 
-        # install pybind
-        bash install_executorch.sh --pybind xnnpack --use-pt-pinned-commit
-
         # install llama requirements
         bash examples/models/llama/install_requirements.sh
 
@@ -543,9 +534,6 @@ jobs:
 
         PYTHON_EXECUTABLE=python bash .ci/scripts/setup-linux.sh "cmake"
 
-        # install pybind
-        bash install_executorch.sh --pybind xnnpack --use-pt-pinned-commit
-
         # install llama requirements
         bash examples/models/llama/install_requirements.sh
 
@@ -573,9 +561,6 @@ jobs:
 
         PYTHON_EXECUTABLE=python bash .ci/scripts/setup-linux.sh "cmake"
 
-        # install pybind
-        bash install_executorch.sh --pybind xnnpack --use-pt-pinned-commit
-
         # install llama requirements
         bash examples/models/llama/install_requirements.sh