Trac #24018: Remove PIP_INSTALL from sage-env

#24014 deprecated the `PIP_INSTALL` environment variable in favor of the
`sdh_pip_install` helper function.  This ticket is to remove
`PIP_INSTALL` entirely.

URL: https://trac.sagemath.org/24018
Reported by: embray
Ticket author(s): Frédéric Chapoton
Reviewer(s): Erik Bray

build/pkgs/dot2tex/dependencies

@@ -1,4 +1,4 @@
-$(PYTHON) | pip
+$(PYTHON) | pip pyparsing
 
 ----------
 All lines of this file are ignored except the first.

build/pkgs/dot2tex/spkg-install

@@ -8,14 +8,15 @@ cd src
 
 # Check that Graphviz is installed by running dot2tex from the source
 # directory.
-python -c "import sys; from dot2tex.dotparsing import find_graphviz; sys.exit(0 if find_graphviz() else 1)"
+sage-python23 -c "import sys; from dot2tex.dotparsing import find_graphviz; sys.exit(0 if find_graphviz() else 1)"
 if [ $? -ne 0 ]; then
     echo >&2 "Error: dot2tex requires Graphviz but Graphviz is not installed. You can download Graphviz at http://www.graphviz.org/Download..php"
     exit 1
 fi
 
-$PIP_INSTALL .
+sdh_pip_install .
+
 if [ $? -ne 0 ]; then
-    echo >&2 "Error installing dot2tex."
     exit 1
 fi
+

src/bin/sage-env

@@ -642,9 +642,6 @@ if [ "${MAKEFLAGS-__unset__}" != "__unset__" ]; then
 fi
 export MAKE
 
-# Deprecated: See https://trac.sagemath.org/ticket/24014
-export PIP_INSTALL="sage-pip-install"
-
 export PIP_FORMAT="columns"
 
 # When building documentation, use MathJax by default. To turn it off,