Remove redundant return @IntDef values

These were causing docs to be generated where the possible values were printed
twice. For example:

Returns one of HDCP_LEVEL_UNKNOWN, HDCP_NONE, HDCP_V1,
HDCP_V2, HDCP_V2_1, HDCP_V2_2 or HDCP_NO_DIGITAL_OUTPUT. Value is
HDCP_LEVEL_UNKNOWN, HDCP_NONE, HDCP_V1, HDCP_V2, HDCP_V2_1, HDCP_V2_2,
or HDCP_NO_DIGITAL_OUTPUT

bug:119280443
Change-Id: I6e8ca3427964b32d6b75aab9fc55239075d13134