docs: Remove needless configure options

Specifying --enable-static --disable-shared isn't necessary, these
are the defaults.
Signed-off-by: Martin Storsjö <martin@martin.st>

doc/general.texi

@@ -1024,7 +1024,7 @@ diffutils
 Then run
 
 @example
-./configure --enable-static --disable-shared
+./configure
 @end example
 
 to make a static build.
@@ -1071,7 +1071,7 @@ and add some special flags to your configure invocation.
 
 For a static build run
 @example
-./configure --target-os=mingw32 --enable-static --disable-shared --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin
+./configure --target-os=mingw32 --extra-cflags=-mno-cygwin --extra-libs=-mno-cygwin
 @end example
 
 and for a build with shared libraries