libe-book: enable strictDeps / parallel building, clean up

The unused function issue was fixed in 0.1.3

https://sourceforge.net/p/libebook/code/ci/8ddc3aff0b6bfc5678ef48d716a99f5aaf385004/

pkgs/by-name/li/libe-book/package.nix

···
   liblangtag,
 }:
 
-stdenv.mkDerivation rec {
+stdenv.mkDerivation (finalAttrs: {
   pname = "libe-book";
   version = "0.1.3";
 
   src = fetchurl {
-    url = "mirror://sourceforge/libebook/libe-book-${version}/libe-book-${version}.tar.xz";
+    url = "mirror://sourceforge/libebook/libe-book-${finalAttrs.version}/libe-book-${finalAttrs.version}.tar.xz";
     hash = "sha256-fo2P808ngxrKO8b5zFMsL5DSBXx3iWO4hP89HjTf4fk=";
   };
 
   # restore compatibility with icu68+
+  # https://sourceforge.net/p/libebook/code/ci/edc7a50a06f56992fe21a80afb4f20fbdc5654ed/
   postPatch = ''
-    substituteInPlace src/lib/EBOOKCharsetConverter.cpp --replace \
+    substituteInPlace src/lib/EBOOKCharsetConverter.cpp --replace-fail \
       "TRUE, TRUE, &status)" \
       "true, true, &status)"
   '';
···
     liblangtag
   ];
 
-  env.NIX_CFLAGS_COMPILE = "-Wno-error=unused-function";
+  strictDeps = true;
+
+  enableParallelBuilding = true;
 
-  meta = with lib; {
+  meta = {
     description = "Library for import of reflowable e-book formats";
-    license = licenses.lgpl21Plus;
-    maintainers = with maintainers; [ raskin ];
-    platforms = platforms.unix;
+    license = lib.licenses.lgpl21Plus;
+    maintainers = with lib.maintainers; [ raskin ];
+    platforms = lib.platforms.unix;
   };
-}
+})