Auto merge of #21992 - steveklabnik:gh17220, r=alexcrichton

None of the others work, so let's remove them.

Fixes #17220.

r? @brson

configure

@@ -653,9 +653,7 @@ probe CFG_GRUN             grun
 probe CFG_FLEX             flex
 probe CFG_BISON            bison
 probe CFG_PANDOC           pandoc
-probe CFG_PDFLATEX         pdflatex
 probe CFG_XELATEX          xelatex
-probe CFG_LUALATEX         lualatex
 probe CFG_GDB              gdb
 probe CFG_LLDB             lldb
 

mk/docs.mk

@@ -85,27 +85,16 @@ else
 HTML_DEPS :=
 endif
 
-# Check for the various external utilities for the EPUB/PDF docs:
-
-ifeq ($(CFG_LUALATEX),)
-  $(info cfg: no lualatex found, deferring to xelatex)
-  ifeq ($(CFG_XELATEX),)
-    $(info cfg: no xelatex found, deferring to pdflatex)
-    ifeq ($(CFG_PDFLATEX),)
-      $(info cfg: no pdflatex found, disabling LaTeX docs)
-      NO_PDF_DOCS = 1
-	else
-      CFG_LATEX := $(CFG_PDFLATEX)
-    endif
-  else
+# Check for xelatex
+
+ifeq ($(CFG_XELATEX),)
     CFG_LATEX := $(CFG_XELATEX)
     XELATEX = 1
-  endif
-else
-  CFG_LATEX := $(CFG_LUALATEX)
+  else
+    $(info cfg: no xelatex found, disabling LaTeX docs)
+    NO_PDF_DOCS = 1
 endif
 
-
 ifeq ($(CFG_PANDOC),)
 $(info cfg: no pandoc found, omitting PDF and EPUB docs)
 ONLY_HTML_DOCS = 1