init: remove extra space in list of bootconfig values

If a bootconfig argument has a list of values, it has a space between
them in /proc/bootconfig.

Example:
BOARD_BOOTCONFIG := parameter=value1,value2,value3

In /proc/bootconfig, it looks like:
parameter = "value1", "value2", "value3"

Before this CL, that example would end up with the value string of:
"value1, value2, value3"

To keep consistent behavior with kernel cmdline the value string should be:
"value1,value2,value3"

Test: Boot cuttlefish with test bootconfig params and verify ro.boot.*
Bug: 192257482
Merged-In: Iccdec451f53330162fa2c9ad2b7c2630f32b4168
Change-Id: Iccdec451f53330162fa2c9ad2b7c2630f32b4168