schema: Remove invalid default values for TEXT columns

When running in strict mode, mysql throws an error upon encountering
these definitions since they are not supported.

References:
https://dev.mysql.com/doc/refman/5.7/en/data-type-defaults.html

Signed-off-by: Florian Pritz <bluewind@xinu.at>
Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

schema/aur-schema.sql

@@ -80,7 +80,7 @@ CREATE TABLE PackageBases (
 	NumVotes INTEGER UNSIGNED NOT NULL DEFAULT 0,
 	Popularity DECIMAL(10,6) UNSIGNED NOT NULL DEFAULT 0,
 	OutOfDateTS BIGINT UNSIGNED NULL DEFAULT NULL,
-	FlaggerComment TEXT NOT NULL DEFAULT '',
+	FlaggerComment TEXT NOT NULL,
 	SubmittedTS BIGINT UNSIGNED NOT NULL,
 	ModifiedTS BIGINT UNSIGNED NOT NULL,
 	FlaggerUID INTEGER UNSIGNED NULL DEFAULT NULL,       -- who flagged the package out-of-date?
@@ -253,7 +253,7 @@ CREATE TABLE PackageComments (
 	ID BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
 	PackageBaseID INTEGER UNSIGNED NOT NULL,
 	UsersID INTEGER UNSIGNED NULL DEFAULT NULL,
-	Comments TEXT NOT NULL DEFAULT '',
+	Comments TEXT NOT NULL,
 	CommentTS BIGINT UNSIGNED NOT NULL DEFAULT 0,
 	EditedTS BIGINT UNSIGNED NULL DEFAULT NULL,
 	EditedUsersID INTEGER UNSIGNED NULL DEFAULT NULL,
@@ -331,8 +331,8 @@ CREATE TABLE PackageRequests (
 	PackageBaseName VARCHAR(255) NOT NULL,
 	MergeBaseName VARCHAR(255) NULL,
 	UsersID INTEGER UNSIGNED NULL DEFAULT NULL,
-	Comments TEXT NOT NULL DEFAULT '',
-	ClosureComment TEXT NOT NULL DEFAULT '',
+	Comments TEXT NOT NULL,
+	ClosureComment TEXT NOT NULL,
 	RequestTS BIGINT UNSIGNED NOT NULL DEFAULT 0,
 	Status TINYINT UNSIGNED NOT NULL DEFAULT 0,
 	PRIMARY KEY (ID),