Revert "Install libpng using pacman instead of manual build for msys2"

This reverts commit dc2e210.

INSTALL.md

@@ -125,19 +125,52 @@ Otherwise, ask for help on Discord or IRC (see [README.md](README.md)), or conti
 
 Note that in msys2, Copy is Ctrl+Insert and Paste is Shift+Insert.
 
-1. Open msys2 at C:\devkitPro\msys2\mingw64.exe or run `C:\devkitPro\msys2\msys2_shell.bat -mingw64`.
+1. Open msys2 at C:\devkitPro\msys2\msys2_shell.bat.
 
 2. Certain packages are required to build pokeemerald. Install these by running the following command:
 
     ```bash
-    pacman -S make zlib-devel git mingw-w64-x86_64-gcc mingw-w64-x86_64-libpng
+    pacman -S make gcc zlib-devel git
     ```
     <details>
         <summary><i>Note...</i></summary>
 
     >   This command will ask for confirmation, just enter the yes action when prompted.
     </details>
 
+3. Download [libpng](https://sourceforge.net/projects/libpng/files/libpng16/1.6.37/libpng-1.6.37.tar.xz/download).
+
+4. Change directory to where libpng was downloaded. By default, msys2 will start in the current user's profile folder, located at **C:\Users\\&#8288;_\<user>_**, where *\<user>* is your Windows username. In most cases, libpng should be saved within a subfolder of the profile folder. For example, if libpng was saved to **C:\Users\\_\<user>_\Downloads** (the Downloads location for most users), enter this command:
+
+    ```bash
+    cd Downloads
+    ```
+
+    <details>
+        <summary><i>Notes...</i></summary>
+
+    >   Note 1: While not shown, msys uses forward slashes `/` instead of backwards slashes `\` as the directory separator.  
+    >   Note 2: If the path has spaces, then the path must be wrapped with quotations, e.g. `cd "Downloads/My Downloads"`.  
+    >   Note 3: Windows path names are case-insensitive so adhering to capitalization isn’t needed.   
+    >   Note 4: If libpng was saved elsewhere, you will need to specify the full path to where libpng was downloaded, e.g. `cd c:/devkitpro/msys2` if it was saved there.
+    </details>
+
+5. Run the following commands to uncompress and install libpng.
+
+    ```bash
+    tar xf libpng-1.6.37.tar.xz
+    cd libpng-1.6.37
+    ./configure --prefix=/usr
+    make check
+    make install
+    ```
+
+6. Then finally, run the following command to change back to the user profile folder.
+
+    ```bash
+    cd
+    ```
+
 ### Choosing where to store pokeemerald (msys2)
 At this point, you can choose a folder to store pokeemerald into. If you're okay with storing pokeemerald in the user profile folder, then proceed to [Installation](#installation). Otherwise, you'll need to account for where pokeemerald is stored when changing directory to the pokeemerald folder.