SIP addresses containing "911" shouldn't be considered emergency calls

This change updates isEmergencyNumberInternal() to always return false if
you pass in a SIP address, since the concept of "emergency numbers" is
only meaningful for calls placed over the cell network.

Previously we *did* try to compare SIP addresses against the list of known
emergency numbers, which caused bad behavior with SIP addresses that even
contained "911"/"112"/etc as a substring (since we were filtering out
non-dialable characters before doing the comparison!)

TESTED:

  - Before this change, calls to "abc911def@example.com" or
    "911abcdef@example.com" were incorrectly detected as emergency
    numbers, and fail.

  - After this change, SIP addresses like "abc911def@example.com" and
    "911abcdef@example.com" work fine.

  - Also, confirmed that this change doesn't break the restriction that
    3rd party apps shouldn't be able to make emergency calls.

    Specifically, I fired off ACTION_CALL intents (using the CallDialTest
    activity) for a bunch of numbers *similar* to emergency numbers, and
    confirmed that none of them actually resulted in an emergency call
    being placed.
    The specific ACTION_CALL intents I tested were:
      "911"         ==> Didn't place the call; brought up dialer instead
      "tel:911"     ==> Didn't place the call; brought up dialer instead
      "911@foo"     ==> Tried to start a SIP call (which failed)
      "911%40foo"     ==> Tried to start a SIP call (which failed)
      "tel:911@foo" ==> Tried to start a SIP call (which failed)
      "tel:911%40foo" ==> Tried to start a SIP call (which failed)
      "911@example.com" ==> Tried to start a SIP call (which failed)
      "sip:911"     ==> Didn't place the call; brought up dialer instead
      "sip:911@foo" ==> Tried to start a SIP call (which failed)
      "sip:911%40foo" ==> Tried to start a SIP call (which failed)

Bug: 5515452
Change-Id: I6f9f8690b08564c53c7a76f480654477b475d94d