Remove unneeded entries from libavfilter.pc

The stagingdir entries are added by the upstream build system due
to linking to lensfun and whisper.cpp static libraries. All these
entries can be removed, alongside with the libraries themselves.

PKGBUILD

@@ -405,4 +405,9 @@ package() {
     make -C "ffmpeg-${pkgver}" DESTDIR="$pkgdir" install
     install -D -m755 "ffmpeg-${pkgver}/tools/qt-faststart" -t "${pkgdir}/usr/bin"
     install -D -m644 LICENSE -t "${pkgdir}/usr/share/licenses/${pkgname}"
+    sed -i \
+        -e 's|-llensfun ||' \
+        -e 's|-lwhisper ||' \
+        -e "s|-L${srcdir}/staging/lib ||g" \
+        "${pkgdir}/usr/lib/pkgconfig/libavfilter.pc"
 }