Revert "SIM Phone Book : Modify update operation"

Not required. Not present in AOSP and spec only mandates
numbser field in SIM but do not mandate the value in number
field which can be null.

This reverts commit 8e743dacced5fdc1a037630089f93ff15b2ed58e

Change-Id: I49749351597118183780ed268fca074349f1e2ab