Simplify ffmpeg dependencies Makefile

The fact that the current prebuilt FFmpeg is split into two separate
zipfiles is an implementation detail.

Use a single Makefile recipe for both files.

PR #2952 <https://github.com/Genymobile/scrcpy/pull/2952>

prebuilt-deps/Makefile

@@ -1,30 +1,24 @@
 .PHONY: prepare-win32 prepare-win64 \
-	prepare-ffmpeg-shared-win32 \
-	prepare-ffmpeg-dev-win32 \
-	prepare-ffmpeg-shared-win64 \
-	prepare-ffmpeg-dev-win64 \
+	prepare-ffmpeg-win32 \
+	prepare-ffmpeg-win64 \
 	prepare-sdl2 \
 	prepare-adb
 
-prepare-win32: prepare-sdl2 prepare-ffmpeg-shared-win32 prepare-ffmpeg-dev-win32 prepare-adb
-prepare-win64: prepare-sdl2 prepare-ffmpeg-shared-win64 prepare-ffmpeg-dev-win64 prepare-adb
+prepare-win32: prepare-sdl2 prepare-ffmpeg-win32 prepare-adb
+prepare-win64: prepare-sdl2 prepare-ffmpeg-win64 prepare-adb
 
-prepare-ffmpeg-shared-win32:
+prepare-ffmpeg-win32:
 	@./prepare-dep https://github.com/Genymobile/scrcpy/releases/download/v1.16/ffmpeg-4.3.1-win32-shared.zip \
 		357af9901a456f4dcbacd107e83a934d344c9cb07ddad8aaf80612eeab7d26d2 \
 		ffmpeg-4.3.1-win32-shared
-
-prepare-ffmpeg-dev-win32:
 	@./prepare-dep https://github.com/Genymobile/scrcpy/releases/download/v1.16/ffmpeg-4.3.1-win32-dev.zip \
 		230efb08e9bcf225bd474da29676c70e591fc94d8790a740ca801408fddcb78b \
 		ffmpeg-4.3.1-win32-dev
 
-prepare-ffmpeg-shared-win64:
+prepare-ffmpeg-win64:
 	@./prepare-dep https://github.com/Genymobile/scrcpy/releases/download/v1.16/ffmpeg-4.3.1-win64-shared.zip \
 		dd29b7f92f48dead4dd940492c7509138c0f99db445076d0a597007298a79940 \
 		ffmpeg-4.3.1-win64-shared
-
-prepare-ffmpeg-dev-win64:
 	@./prepare-dep https://github.com/Genymobile/scrcpy/releases/download/v1.16/ffmpeg-4.3.1-win64-dev.zip \
 		2e8038242cf8e1bd095c2978f196ff0462b122cc6ef7e74626a6af15459d8b81 \
 		ffmpeg-4.3.1-win64-dev