[doc] Soften the warnings around Anaconda (RobotLocomotion#19515)

Remove pip known issues (all fixed).

doc/_pages/installation.md

@@ -35,12 +35,10 @@ require a working display server.  Most personal computers will have this
 already built in, but some cloud or docker environments may require extra
 setup steps.
 
-⁽²⁾ CPython is the only Python implementation supported. Drake does not support
-the Python environment supplied by Anaconda. Before installing or using Drake,
-please `conda deactivate` (repeatedly, until even the conda base environment has
-been deactivated) such that none of the paths reported `which -a python python3`
-refer to conda. Note that Miniconda seems to work fine; it's only Anaconda that
-has caused problems for some users.
+⁽²⁾ CPython is the only Python implementation supported.
+Drake is not tested regularly with Anaconda, so if you are using Anaconda you
+may experience compatibility hiccups; when asking for help, be sure to mention
+that Conda is involved.
 
 ⁽³⁾ The Python version shown in the table is supported for all installation
 channels. Additionally, on Ubuntu when installing via ``pip`` Python versions

doc/_pages/pip.md

@@ -27,22 +27,10 @@ in [Source Installation](/from_source.html).
 
 ## Stable Releases
 
-<div class="warning" markdown="1">
-Drake does not support the Python environment supplied by Anaconda. Before
-installing or using Drake, please `conda deactivate` (repeatedly, until even
-the conda base environment has been deactivated) such that none of the paths
-reported `which -a python python3 pip pip3` refer to conda.
-Note that Miniconda seems to work fine; it's only Anaconda that has caused
-problems for some users.
-</div>
-
-<div class="warning" markdown="1">
-Drake's support for pip has a few known issues (see
-[issue #15954](https://github.com/RobotLocomotion/drake/issues/15954)).
-Please [let us know](/getting_help.html) if you
-experience any additional problems. To fall back to other installation methods
-in the meantime, refer to [Installation and Quickstart](/installation.html)
-for more choices.
+<div class="note" markdown="1">
+Drake is not tested regularly with Anaconda, so if you are using Anaconda you
+may experience compatibility hiccups; when asking for help, be sure to mention
+that Conda is involved.
 </div>
 
 We recommend installing drake into a

doc/_pages/python_bindings.md

@@ -15,13 +15,10 @@ class which is exposed to C++ has been explicitly enumerated in one of the
 source files inside the ``bindings/pydrake`` folder. These bindings are
 installed as a single package called ``pydrake``.
 
-<div class="warning" markdown="1">
-Drake does not support the Python environment supplied by Anaconda. Before
-installing or using Drake, please `conda deactivate` (repeatedly, until even
-the conda base environment has been deactivated) such that none of the paths
-reported `which -a python python3 pip pip3` refer to conda.
-Note that Miniconda seems to work fine; it's only Anaconda that has caused
-problems for some users.
+<div class="note" markdown="1">
+Drake is not tested regularly with Anaconda, so if you are using Anaconda you
+may experience compatibility hiccups; when asking for help, be sure to mention
+that Conda is involved.
 </div>
 
 # Installation

setup/mac/binary_distribution/install_prereqs.sh

@@ -26,7 +26,7 @@ if [[ "${EUID}" -eq 0 ]]; then
 fi
 
 if command -v conda &>/dev/null; then
-  echo 'WARNING: Anaconda is NOT supported for building and using the Drake Python bindings' >&2
+  echo 'NOTE: Drake is not tested regularly with Anaconda, so you may experience compatibility hiccups; when asking for help, be sure to mention that Conda is involved.' >&2
 fi
 
 if ! command -v brew &>/dev/null; then

setup/ubuntu/binary_distribution/install_prereqs.sh

@@ -38,7 +38,7 @@ fi
 
 
 if command -v conda &>/dev/null; then
-  echo 'WARNING: Anaconda is NOT supported for building and using the Drake Python bindings' >&2
+  echo 'NOTE: Drake is not tested regularly with Anaconda, so you may experience compatibility hiccups; when asking for help, be sure to mention that Conda is involved.' >&2
 fi
 
 binary_distribution_called_update=0