Fix deprecated pytorch_sphinx_theme editable installation (#145347)

Fixes #145221

Pip editable install is going to be deprecated soon pypa/pip#11457.  The fix here is just to remove it and install `pytorch_sphinx_theme` normally.

### Testing

Doc build is working with the change:

* PR https://github.com/pytorch/pytorch/actions/runs/12901499736/job/35975042345?pr=145347
* Nightly https://github.com/pytorch/pytorch/actions/runs/12901500521/job/35975046289
Pull Request resolved: #145347
Approved by: https://github.com/ZainRizvi

.ci/docker/requirements-docs.txt

@@ -1,7 +1,7 @@
 sphinx==5.3.0
 #Description: This is used to generate PyTorch docs
 #Pinned versions: 5.3.0
--e git+https://github.com/pytorch/pytorch_sphinx_theme.git#egg=pytorch_sphinx_theme
+git+https://github.com/pytorch/pytorch_sphinx_theme.git#egg=pytorch_sphinx_theme
 
 # TODO: sphinxcontrib.katex 0.9.0 adds a local KaTeX server to speed up pre-rendering
 # but it doesn't seem to work and hangs around idly. The initial thought is probably

docs/requirements.txt

@@ -1,5 +1,5 @@
 sphinx==5.0.0
--e git+https://github.com/pytorch/pytorch_sphinx_theme.git#egg=pytorch_sphinx_theme
+git+https://github.com/pytorch/pytorch_sphinx_theme.git#egg=pytorch_sphinx_theme
 # TODO: sphinxcontrib.katex 0.9.0 adds a local KaTeX server to speed up pre-rendering
 # but it doesn't seem to work and hangs around idly. The initial thought is probably
 # something related to Docker setup. We can investigate this later