Updated Tree/AVLTREE.c with cross-platform compatibility

[Haricodezz]

fix: replace non-standard clrscr() with portable console clear alternative

• Removed use of clrscr(), which is not part of the standard C library and causes compatibility issues across compilers and OS.
• Added comments suggesting portable alternatives: system("cls") for Windows and system("clear") for Unix-like systems.
• Updated code to use system-specific command with optional preprocessor condition for cross-platform support.

This ensures the AVL Tree program compiles and runs correctly in standard C environments.

// clrscr();
// Replaced clrscr() with system-specific clear command for portability.
#ifdef _WIN32
system("cls"); // Clear screen on Windows
#else
system("clear"); // Clear screen on Unix-like systems
#endif