doc: Use the C file as source instead of the lex file

Doxygen does not seem to handle lex source files nicely, but because the
functions to document are marked in the header anyway, only those should
end up in the final documentation.

doc/Doxyfile.in

@@ -591,8 +591,7 @@ INPUT_ENCODING         = UTF-8
 # *.hpp *.h++ *.idl *.odl *.cs *.php *.php3 *.inc *.m *.mm *.py *.f90
 
 FILE_PATTERNS          = *.c \
-                         *.h \
-                         *.l
+                         *.h
 
 # The RECURSIVE tag can be used to turn specify whether or not subdirectories
 # should be searched for input files as well. Possible values are YES and NO.
@@ -604,7 +603,7 @@ RECURSIVE              = YES
 # excluded from the INPUT source files. This way you can easily exclude a
 # subdirectory from a directory tree whose root is specified with the INPUT tag.
 
-EXCLUDE                = lib/dpkg/trigdeferred.c
+EXCLUDE                =
 
 # The EXCLUDE_SYMLINKS tag can be used select whether or not files or
 # directories that are symbolic links (a Unix filesystem feature) are excluded