[host_memory] remove unused fastmem fallback path (#3133)

basically nobody ever used that path, we instead soft-crash upon not being able to allocate **backing** storage, we do still attempt to allocate a virtual base through, but if backing storage fails for any reason whatsoever, we pretty much cant run the emulator anyways

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3133
Reviewed-by: DraVee <dravee@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

src/common/host_memory.h

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2019 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -79,9 +82,6 @@ private:
     u8* backing_base{};
     u8* virtual_base{};
     size_t virtual_base_offset{};
-
-    // Fallback if fastmem is not supported on this platform
-    std::unique_ptr<Common::VirtualBuffer<u8>> fallback_buffer;
 };
 
 } // namespace Common