system/gd: Remove unimplemented Module virtual methods

- void Module::GetDumpsys() const
- void Module::GetDumpsys(int fd) const
- void Module::GetDumpsys(std::ostringstream& oss) const

These methods are never meaningfully implemented.
Having multiple GetDumpsys() methods (4!) makes it confusing
to know which should be implemented.

Bug: 333555245
Test: m com.android.btservices
Flag: EXEMPT, no-op change
Change-Id: I031ddff1a44054053acead7a1ff50d50b3fca426