Kernel: Don't require AnonymousFiles to be mmap'd completely

AnonymousFile always allocates in multiples of a page size when created
with anon_create. This is especially an issue if we use AnonymousFile
shared memory to store a shared data structure that isn't exactly a
multiple of a page in size. Therefore, we can just allow mmaps of
AnonymousFile to map only an initial part of the shared memory.

This makes SharedSingleProducerCircularQueue work when it's introduced
later.

Kernel/FileSystem/AnonymousFile.cpp

@@ -22,9 +22,6 @@ ErrorOr<Memory::Region*> AnonymousFile::mmap(Process& process, OpenFileDescripti
     if (offset != 0)
         return EINVAL;
 
-    if (range.size() != m_vmobject->size())
-        return EINVAL;
-
     return process.address_space().allocate_region_with_vmobject(range, m_vmobject, offset, {}, prot, shared);
 }