removed unused which function in CI scripts (#3095)

tools/ci/gha-install.py

@@ -2,22 +2,6 @@
 import shutil
 import subprocess
 
-def which(program):
-    def is_exe(fpath):
-        return os.path.isfile(fpath) and os.access(fpath, os.X_OK)
-
-    fpath, fname = os.path.split(program)
-    if fpath:
-        if is_exe(program):
-            return program
-    else:
-        for path in os.environ["PATH"].split(os.pathsep):
-            path = path.strip('"')
-            exe_file = os.path.join(path, program)
-            if is_exe(exe_file):
-                return exe_file
-    return None
-
 
 def install(omp=False, mpi=False, phdf5=False, dagmc=False, libmesh=False, ncrystal=False):
     # Create build directory and change to it