Everywhere: Switch from (void) to [[maybe_unused]] (#4473)

Problem:
- `(void)` simply casts the expression to void. This is understood to
  indicate that it is ignored, but this is really a compiler trick to
  get the compiler to not generate a warning.

Solution:
- Use the `[[maybe_unused]]` attribute to indicate the value is unused.

Note:
- Functions taking a `(void)` argument list have also been changed to
  `()` because this is not needed and shows up in the same grep
  command.

Libraries/LibC/unistd.cpp

@@ -515,11 +515,8 @@ int mknod(const char* pathname, mode_t mode, dev_t dev)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
-long fpathconf(int fd, int name)
+long fpathconf([[maybe_unused]] int fd, [[maybe_unused]] int name)
 {
-    (void)fd;
-    (void)name;
-
     switch (name) {
     case _PC_PATH_MAX:
         return PATH_MAX;
@@ -530,10 +527,8 @@ long fpathconf(int fd, int name)
     ASSERT_NOT_REACHED();
 }
 
-long pathconf(const char* path, int name)
+long pathconf([[maybe_unused]] const char* path, int name)
 {
-    (void)path;
-
     switch (name) {
     case _PC_PATH_MAX:
         return PATH_MAX;
@@ -614,9 +609,8 @@ void sysbeep()
     syscall(SC_beep);
 }
 
-int fsync(int fd)
+int fsync([[maybe_unused]] int fd)
 {
-    UNUSED_PARAM(fd);
     dbgprintf("FIXME: Implement fsync()\n");
     return 0;
 }