You can't without editing the module and removing it. You can find the module at the below location.
/modules/mod_cblogin/mod_cblogin.php
It uses JS to remove and restore the value on focus and blur when compact mode is used. I can not help you with this however as we do not support core edits. Best I can suggest is where to find it below.
ON: Lines 660 - 673
Code:
$bgstyleUser .= " alt=\"" . htmlspecialchars( $userNameText ) . "\" value=\"" . htmlspecialchars( $userNameText ) . "\" "
. "onfocus=\"if (this.value=='" . addslashes( $userNameText ) . "') this.value=''\" onblur=\"if(this.value=='') { this.value='" . addslashes( $userNameText ) . "'; return false; }\""
;
$bgstylePass .= " alt=\""._UE_PASS."\" value=\"paswww\" onfocus=\"if (this.value=='paswww') this.value=''\" onblur=\"if(this.value=='') { this.value='paswww'; return false; }\""
;
krileon
