Rip out Boehm GC support.

This is done to simplify memory management across the boundary between C and
Rust. While rewriting WINGs, we may want to be able to malloc/free with the libc
allocator on both sides of that divide.

doc/build/Compilation.texi

@@ -253,14 +253,6 @@ If found, then the library @emph{WRaster} can use the @emph{ImageMagick} library
 @sc{Window Maker} support more image formats, like @emph{SVG}, @emph{BMP}, @emph{TGA}, ...
 You can get it from @uref{http://www.imagemagick.org/}
 
-@item @emph{Boehm GC}
-
-This library can be used by the @emph{WINGs} utility toolkit to use a
-@cite{Boehm-Demers-Weiser Garbage Collector} instead of the traditional
-@command{malloc}/@command{free} functions from the @emph{libc}.
-You have to explicitly ask for its support though (@pxref{Configure Options}).
-You can get it from @uref{http://www.hboehm.info/gc/}
-
 @end itemize
 
 
@@ -468,8 +460,6 @@ You can find more information about the libraries in the
 @ref{Optional Dependencies}.
 
 @table @option
-@item --enable-boehm-gc
-Never enabled by default, use Boehm GC instead of the default @emph{libc} @command{malloc()}
 
 @item --disable-gif
 Disable GIF support in @emph{WRaster} library; when enabled use @file{libgif} or @file{libungif}.