Enhancements for rpcChannel library.

Enhancements for rpcChannel library.

rpcChannel.c file contains the code for building rpcChannel library. A good
amount of the same code is duplicated in rpcChannelSimple.c file to
build a simplified version (no glib dependency) of the rpcChannel library.
It's recommended to remove the duplication and maintain only one single
file which can be used to build both 'glib-dependent rpcChannel' and
'glib independent rpcChannel' library.

This changeset implements the following changes:
* Removed rpcChannelSimple.c

* Renamed I_USE_SIMPLE_RPC make variable to USE_RPCI_ONLY. If this
flag is specified, rpcChannel library will be built using only RPCI.
No dependencies on rpcIn will be added. This inturn will remove
dependencies on dynxdr, xdr and glib.

* Modified the RpcChannelInt structure to have only the necessary
attributes when USE_RPCI_ONLY is defined.

* Modified a bunch of functions into '#if defined(NEED_RPCIN)' block
to make available only when necessary.

* Modified guestrpc.h to provide the declarations for few RpcChannel_*
functions only when needed.

* Modified rpcChannel library to implement necessary stub files / functions
when it has to be built 'with rpci only' setting.

* Removed various copies of 'glib_stubs.c' maintained by different
consumers of rpcChannel (appmonitorlib, vmGuestLib, 'imgcust' components).

* Modified the make files of various consumers (vmGuestLib, appmonitorlib,
imgcust components [linux-pkg-deployer, guestcustutil, UnitTest]) to
remove the dependencies for dynxdr library.

* Did some code refactoring.
- Removed some dead code in some make files.